Look at your processes for anything running that seems dodgy and is named any 5 random characters. For example, they could be named ntee2.exe. If you have something like that, then you have the trojan spyware that so far circumvents all blockers, adaware, spybot, and other such adware detecting tools, and cannot be easily removed. I can supply removal instructions if you have anything like that.
Also, in you Add/Remove Programs, do you have anything called "Home Search Assistent"?? (Yes, assistent, spelled with an "e" )