If you want to access your AOL Instant Messenger account at a computer without iChat, AIM, or one of the various third party clients installed, you can always use AIM Express. However, according to its website, Safari isn't supported, and therefore cannot launch the applet.
I did some investigating, mostly by disguising Safari as MSIE 6.0 and bypassing the JavaScript checks. It turns out that AIM Express does work in Safari, and pretty much flawlessly. You don't even need the Debug Menu activated. Here's how to (hopefully) get AIM Express running on an unsupported browser, in three (easy?) steps.
Note: I didn't test this with .Mac screennames. I don't imagine it'd be any different, but somewhere along the line it might reject the @ symbol in the screenname. Furthernote that this has only been tested on Safari.
mWin.document.location = "http://aimexpress.oscar.aol.com/
aimexpress/launch.adp=&siteId=aimexpressprod&siteState=&mcAuth=
z%252Bq7hML2MDhdtBF8AdILpQ%253D%253D%2ddiAxLjAga2lkIDIwMDQwNzI5M
DEwMDAzMDQADXCw%253D%253D%2dxUwMcVB%252FvVFhKk1lzV9uNpj49DFnX8qJ
8QpkjlsF5bZidYuHXqQMIDsT1KbozsG6E59PDqwQ6SacbV5J%252ByOrTHZ8lmD2
ekF8tdjVxt%252BIK68DgV%252B7DY8AztbR%252B7gycpB55dP5otdLrVChUJ%2
52Bk7rA%253D%253D&interWidth=270&interHeight=180&"
Note that if you see any errors, some of them must be closed with the red "close" titlebar widget -- hitting the OK button on these troublesome errors simply makes the message pop up again.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20040729200648505