Whether AOL's own figure of 150 million-plus users or figures from Jupiter Research (18.6 million for AIM alone vs. 9.5 million for Yahoo Messenger as of Sept. 2001) are believed, its plainly evident that the AIM network dwarfs Yahoo's.

AOL's AIM client, though, took a seat behind Yahoo's in terms of advertising and marketing potential. Yahoo's leg-up came in the form of Yahoo IMVironments -- interactive, themed backgrounds for the Yahoo Messenger client that appear directly in the IM window. Yahoo has been selling the heck out of these things to companies like Glaxo SmithKline, RadioShack, Purina, E*Trade and Kellogg's.

AOL, meantime, only offered a few box ads in its Buddy List. It also gave companies the chance to entice AIM users to use branded Buddy Icons as their own. An AIM'er, for example, can use icons from movies like Austin Powers in Goldmember or fear dot com.

Now, AOL is most definitely catching up with Yahoo, marketing-wise, with its newest version of the AIM client.

Currently in beta, the client includes "AIM Expressions," downloadable "themes" that add graphics and animation to users' "Buddy List" and chat windows. In the beta version, three generic themes exist -- Patriotic, Red Rose and Evil. A general form of "Expression" is also available.

It's the Expression for the recently released Eight Legged Freaks, though, that marketers should pay attention to. That Expression shows advertising creative in a thin vertical strip of space alongside users' Buddy List window, which users often leave permanently visible on the side of their screens. Ad space is also used in users' chat windows. In addition, the user's own Buddy Icon -- visible to chat partners -- is automatically set to coordinate with the promotional theme. In the case of Eight Legged Freaks, a large black spider appears on a bright yellow background.

AIM 5.0 marks the first time that AOL has placed advertising on the chat window itself. But the company said it is reluctant to intrude too heavily on the user experience in the IM window, and especially in the space where users type to each other. "That area is somewhat sacred to us and our users, so you're not going to see extensive use there," AOL spokesperson Derick Mains told InternetNews.com last month.

Mains declined to comment in detail on the company's plans to offer advertising space on AIM 5.0. "Right now, we're just testing the feature and looking to get feedback from users," he said. "Then we'll determine where we go from there from a business standpoint."

Evidentially, the "business standpoint" is winning the Expressions battle at AOL. As of today, Old Navy (with its new "Rugby Bunch" promotion a-la the Brady Bunch) and NASCAR.com are now available in the downloadable Expressions list, available directly from within the 5.0 beta client. Clicking on the Brady Bunch-style windows from within the Buddy List window takes the user to the main OldNavy.com Web site. The same real estate in the NASCAR.com Expression, meantime, has two links -- one to the NASCAR.com e-commerce site, and another to Dale Earnhardt Jr.'s NASCAR.com Web page.

The enhancements to AIM's newest version also give AOL an opportunity to expand the rich media capabilities it can offer to clients. Courtesy of AOL's partnership with rich-media graphics firm Viewpoint, a giant animated spider periodically creeps out from users' chat windows and across their desktops.

Since the New York-based firm's media player is downloaded simultaneously with much of AOL's software -- such as the new version 7.0 of its proprietary Internet service, or when users elect to download the "Freaks" theme -- sources close to the firms say that opens the door for such rich media features to be offered for future AIM ads.

Other new features include the ability to see stocks, news, entertainment and expressions in the Buddy List, and a sorely needed Typing Indicator to see when a person is physically responding to your instant message. Both parties in the IM conversation need to have AIM 5.0 to enable the Typing Indicator.

Also, functions like "Get Info" on a buddy and "Setup" are now on the Buddy List window; previously, users had to go into the menu structure to access those features.

The final version of the AIM 5.0 client is expected to be rolled out late this summer.

InternetNews.com Senior Editor Christopher Saunders contributed to this article. Bob Woods is the managing editor of InstantMessagingPlanet.