There is a lot of it about at the moment and if you look on YouTube you will see various explanations of how to remove it, unfortunately they are mainly stupid and may leave you worse off than you started as they only address a small part of the problem.
I know those people are trying to help folks but they are obviously not qualified to do so. The malware programs in question Antivirus XP 2008 /2009 will download other stuff to your computer and they do not always do the same thing so deleting a couple of files and a folder or two isn't going to help you - for long.
It seems that both Malwarebytes AntiMalware (free version) and SuperAntiSpyware (free version) both now have removal scripts that work so if you are willing to install a program temporarily to remove the problem these two will address both the fake antivirus and any downloaded crapware that it has further infected your computer with. They should also fix the Policies that the infection adds (can't change desktop/open regedit/open task manager).
There is also a useful script for these types of infections maintained by a guy at internetinspiration http://www.internetinspiration.co.uk/roguefix.htm which will help you if you have an alternate antispyware that hasn't yet added defs for the Antivirus XP 200x.