It isn't trying to install "Antivirus XP 2008" by any chance, is it? This thing is all over the place. If so, there are lots of directions to remove it online, including here: http://www.bleepingcomputer.com/malware-removal/remove-antivirus-xp-2008

You probably need to start in Safe Mode, stop the application from running, then start deleting it and strip it from your registry. You also should run some spyware removing software: Malwarebytes' Anti-Malware is recommended.

Good luck! These things suck.