You have malicious code, Ad-aware will not necessarily pick up on this one. You've picked up some malicious code which IE 5.0 is really VENERABLE to. It's on a lot of slightly dodgy websites (you know the ones, not overtly illegal (although closer inspection leads you to get out very fast), and offering seemingly loads of sex site content and not having those sign up screens).
You will NOT get rid of this with on-line checkers, security updates, etc. It's code sitting on your system, which probably gets executed everytime you start IE.
You have two options. Format and reinstall or try a different browser. Mozilla.org, opera.com, Netscape (and there are others), remeber to configure your preferences after install, it makes a difference.
Remove the IE executable after you have your new browser so no one else can start up and see the same offensive material. Then find something else to do with your life rather than surf sex sites. Like using your computer, because it's a powerful tool. And then find out about Linux and Unix and Macs.