Windows is often victemized by trojans. Here's a few programs that may find and destroy your infection.

• Malwarebytes is my favorite for now (as of early 2010). It's best to go to Download.com and search for it by name.
• SuperAntiSpare works, is free and deosn't seem to harass the user too much once installed. There is a commercial version, and you may receive offers to upgrade occasionally when you manually update the software.
• Combofix is very simple (and free), practically no interraction at all. Don't be too put off by the DOS looking screens.
• Spybot Search and Destroy does the job.