Like the guys say, Download Ad-Aware 6.0. You can get the Pro version off Kazaa or just PM me and I'll send it to you.
Also, after you've ran Ad-Aware go into your Program Files folder. But I suggest doing this only if you know what you're doing. There's always some left over files that get downloaded / installed on your system. They're safe to delete.
One for instance is ISTBar. You can get this junk from visiting sites like
http://astalavista.box.sk - for finding serial numbers / cracks. Once you enter something to search for it'll give you a list of sites that have matches. Click on a site and it'll bring up the files and in order to download, you have to install some shit, which ends up being more than you want.
And if you really know what you're doing, you can delete the files from your registry using Regedit. But don't mess with the registry if you're a novice user.