AIM:
By far the most popular Instant messenger. It has most of the capabilities of every other IM. You can IM, Chat, share files, share pix, use webcams, and share photos.
To find out more info, click here:
http://www.aim.com/
To download, click here:
http://download.newaol.com/aim/win95/Install_AIM.exe
To get a screen name, click here:
https://reg.my.screenname.aol.com/_cqr/registration/initRegistration.psp