You don't have a virus, and in most cases, AntiVirus software isn't going to help you. You have malware/spyware. This is what's known as a fake AntiVirus or Fake AntiSpyware program. It's purpose is to get your credit card info.
You can run an AntiVirus program and it may detect and remove certain files that it perceives as a threat, but it won't fix the system files and registry changes that have already been made.
Your best and easiest solution is to wipe and load with your restore disk if you have one. If not, download and run a program like "SuperAntiSpyware" and let it detect and delete the hidden files that are causing the problem. Still, in most cases this won't fix the registry changes that were made to limit your admin control. These changes were made to keep you from removing the program.
If you decide not to wipe and load and go with the spyware remover, you will still need to find rouge files and fix settings and registry keys when it's done. I don't think it's something that can be explained. You have to do it on-the-fly.
If your lucky, the spyware remover will identify the program and you may find a downloadable fix/remover for the rest of the problems. Be careful, many times what looks like a valid fix or program is actually more spyware and can make the problem worse.
Brian.