Just use an Internet-based service so that you can chat from a Web page without having to install any software, which might be blocked by a firewall. I tested two such services: Meebo at www.meebo.com and KoolIM at www.koolim.com. Both are free.

These services let you simultaneously log in to multiple IM accounts — and communicate with people with various services. If you have a friend who uses Yahoo Messenger, for example, and another who likes MSN Messenger, you can chat with either.

Another plus: Meebo and KoolIM are far less vulnerable to viruses than downloadable applications. They’re also more efficient, saving users the hassle of installing multiple programs on a computer. This is especially handy for people with old computers that slow down when running several applications.

Meebo has a well-designed, sleek interface that makes it appealing to even the least tech savvy. From its home page, you simply sign in for different IM services—MSN Messenger, Yahoo Messenger, GTalk (or Jabber) and AIM (or ICQ). Your buddy list will be combined automatically. You don’t have to register, but if you do, you get perks such as a single sign-on for all of your accounts, and the ability to share files, save chat logs and store conversations.

I tried Meebo on my work Windows PC and my iBook at home, and it worked well on both. To start chatting, you just log in to any of the IM services by entering the screen name and password you already have with a service, or by picking a new name, password and services. Your buddy list will appear in a window on the right side of the page, with each name marked by an icon denoting the service the person uses. Once in your buddy list, you can add or delete a contact, message or join a group chat.

The service also offers MeeboMe, a way to chat from your own Web site. Bloggers can use this to start a conversation with site visitors who log in to their Meebo account. It also shows how many users are on the site at any time.

But Meebo, like most such Web services, lacks the ability for audio and video chats — basic features on installed IM software. If you’re used to plugging in a Webcam and headgear to chat with friends, these services might not be for you. Meebo also doesn’t have the standard send button that’s on installed IM software. Instead, you press a key on your keyboard.

Sharing files using Meebo is tricky, too. Only Meebo account holders can send files; although anyone can receive them. When I sent a PDF file to my friend on her installed MSN Messenger, she received a message and a link that rerouted her to Meebo’s home page with no further guidance. When I sent her the same file after she logged in to her MSN using Meebo, she could open the file.

KoolIM also connects users to multiple IM accounts from one Web page. It gives you the option to create an online account, so you don’t need separate log-ins for each IM service you’ll encounter.

You can select an embedded or a pop-up version of the service. The embedded version shows your buddy list and messages as windows tied to a Web page, while the pop-up version lets you move the windows around the screen. You can choose to display all of your buddies or only the ones online. In your buddy-list window you can add and delete names and log in to or out of a service.

I didn’t like having text ads appear at the bottom of the IM window in KoolIM, or the fact that, unlike Meebo, there isn’t a time stamp on messages to tell you when they arrived. It also doesn’t allow you to send files, as Meebo does. And it doesn’t let you save conversations or chat logs. KoolIM’s lack of some of these basic features might make it less appealing to consumers, especially those who ponder swapping it with their desktop software.

I preferred Meebo, but both services are good alternatives to installed IM, if you’re willing to do without audio and video features.

Walt Mossberg is on vacation. Find all my columns and videos online free at the new All Things Digital Web site, http://walt.allthingsd.com.

• Email me at Sarmad.Ali@wsj.com.

On the high end are two versions of the MacBook Pro, which replaces the PowerBook. And for more price-conscious consumers, Apple has just added the MacBook, to replace the iBook.

I reviewed the MacBook Pro earlier this year, and lately I’ve been testing the new MacBook, a handsome machine that packs a very good screen and keyboard into a fairly thin enclosure and is surprisingly inexpensive.

There’s a lot to like about the MacBook. It’s a very good choice for anyone considering a Mac and operating on a tight budget. Like the other Intel-based Macs, it can even run Windows alongside Apple’s own Mac OS X operating system. But it is missing some key features that are standard on Windows-based laptops, and it is heavy compared with its closest Windows competitor.

The first thing you notice about the MacBook is its sharp, vivid 13.3-inch screen, which is larger than the 12.1-inch displays in the latest rash of relatively small Windows laptops. The MacBook screen is glossy, which makes for sharper contrast. Such screens can be subject to annoying reflections, but I didn’t find that to be a problem.

Another striking feature is the keyboard, which uses widely spaced keys that have flat tops, instead of the usual curved surfaces. It looks great, but I worried it would make typing clumsier. Again, that wasn’t a problem.

The MacBook also has a built-in camera, a built-in slot-loading DVD drive, and Intel’s new Core Duo processor, which packs the equivalent of two chips into one. There are three basic configurations, ranging from $1,099 to $1,499, and you can configure each to your specifications. Two of the configurations come in a white case. The top version is black and costs $150 more than a comparably equipped white model.

Perhaps the most surprising thing about the MacBook is its price. Despite Apple’s reputation for charging more, the MacBook is actually less expensive than its closest major Windows competitor. That would be the Sony Vaio VGN-SZ240, which also has a 13.3-inch screen with the same resolution, includes a built-in camera, and is available with the same processor and the same memory and hard-disk capacity as the MacBook.

When configured to match the major specs of the base model of the MacBook, the Sony costs $1,629, over 60% more than the MacBook’s $1,099 base price. But the MacBook is much heavier than the Sony. It weighs 5.2 pounds, 37% more than the Sony’s 3.8 pounds.

In my tests, the MacBook proved to be very snappy. Internet performance over my Wi-Fi network was excellent. Microsoft Office ran very well, as did the Firefox Web browser, Adobe Reader and everything else I tested.

On my tough battery test, where I turn off all power-saving features and keep the hard disk spinning and the screen at maximum brightness, the MacBook lasted three hours and 47 minutes. That suggests you could get nearly five hours with power-saving on and a more normal usage pattern. A high-end model of the much costlier Sony, which I tested in April, lasted only three hours and two minutes.

And like all Macs, the MacBook is vastly superior to Windows machines in terms of bundled software and security. Apple’s operating system is better designed, more stable and more modern than Windows XP. Its built-in iLife suite of multimedia software can’t be matched on Windows. And it has — so far — been attacked by only two viruses, compared with the more than 100,000 viruses and spyware programs that plague Windows. Those qualities are worth hundreds of dollars, in my view.

Like all Mac laptops, the MacBook lacks a right-click button, even though Apple’s own software displays right-click menus. To emulate a right click, Mac users typically must hold down the Control key while clicking the sole button. But the MacBook has a new way to do this that’s simpler: Place two fingers on the touch pad and click with a third. It works well. The MacBook also has Apple’s very cool scrolling feature, which allows you to scroll any screen by moving two fingers over the touch pad. It’s better than any Windows laptop scrolling feature I’ve seen.

But the MacBook lacks two important hardware features that are nearly ubiquitous on Windows laptops. It has no slots for the flash memory cards used in digital cameras, smart phones and other devices. And it lacks a card slot for the adapters that can provide laptops with many add-on features, including flash memory sockets and cellphone data modems.

The lack of the card slot is particularly nettlesome. Among Apple laptops, only the costlier MacBook Pro has one. Every computer maker seeks to differentiate its low-priced and high-priced products. But withholding a near-universal industry-standard feature from a consumer machine is a bad way to do this. Even Dell’s $499 laptop has a card slot. So if you buy a MacBook, you’ll need to connect your camera with a cable, and to do without some add-on features that require a card slot.

Despite these drawbacks, the MacBook is a solid machine at a great price.

• Email me at mossberg@wsj.com.