In case it is a virus, try downloading and running Stinger. It is a virus removal tool made by McAfee.
You can get it here:
http://us.mcafee.com/virusInfo/default.asp?id=stinger
Microsoft has a similar tool, check out their website too.
If you don't already have anti-virus software, I recommend Avast. It is free, and very good:
http://www.avast.com/ (they also have an 'on-site' virus cleaner)
Microsoft has a similar tool, check out their website too.
You might also want to install some trial versions of anti-spyware. I suggest Counter-Spy and Webroot (Spy Sweeper). Both trials give you fully functioning versions of the software; which will be enough to clean your computer from spyware if it is infected.
http://www.webroot.com/consumer/products/spysweeper http://www.sunbelt-software.com/CounterSpy.cfm
If you are tech-oriented you can also try Hijack This. Running this allows you to see irregularities in your registry.
http://www.majorgeeks.com/download3155.html
Note: I did not click on the link... I'm paranoid
