run "Ad-aware", "Spybot search&destoy", "CWShreder" and your antivirus form safe mode, make sure you update them first!. then reboot back to normal mode and download Hijack This from here:
http://www.spywareinfo.com/~merijn/downloads.html
unzip Hijack This to a permanent folder such as C:\HijackThis. make sure you can view hidden files and folders, including system files. close all open windows. run Hijack This and post you log. this way people veiwing this can get a better idea of what the solution may be, which files to delete etc.