I presume you've tried Ad-Aware. If not do it now and if that doesn't work try installing trial version of spysweeper at click here
Also go to add/remove programs and see if it is in there and try removing. If I remember rightly it would only remove after I had run spysweeper. Can be a tricky one - stick with it.
Oh, and after install and run Ccleaner at click here and scan for issues to make sure all reminents are gone, just make sure you back up before you fix issues (It prompts you to).