Help! My computer is infected with Microsoft Antivirus 2009?

My computer was fine yesterday, then I let my roommate use it. Now I keep getting prompts for this Microsoft Antivirus 2009 download and my system keeps freezing (I have an HP). I deleted my cookies and temporary internet files. I ran my Norton Antivirus Scan and it claims it fixed the problem and that everything is fine with my system but this thing is not really gone. I was searching on here and found manual instructions to get rid of it but it seems intimidating to me (I’m not very tech savvy). I also saw suggestions for these spyware removal websites that can get rid of this virus. Do these sites really work? If so, which one should I use? I also noticed people mentioning that I should remove the virus with computer in “safe mode”, what is this? I am beside myself with worry and I don’t want my personal info stolen. Any suggestions would be greatly appreciated.

safe mode:

http://www.computerhope.com/issues/chsafe.htm

How to remove Antivirus 2009 (Uninstall Instructions)

http://www.bleepingcomputer.com/malware-removal/uninstall-antivirus-2009

Its free & it does work.

Xbox 360 Microsoft Point Generator!! 2009