Major computer help! (VIRUS!) WIN XP?

Hi, I've encountered a problem with this stupid spyware called Win XP 11 home security or something like that. I KNOW it's not legit, it's spyware. I honestly do NOT know how it came here. Ok, so, I got the virus, then I've ran a system restore to three days ago. It was working fine last night until I got the virus AGAIN at the EXACT same time as i got it two days ago. (Does this make sense to you? Might sound a little weird.) It suddenly overrides my firewall, and my ESET NOD32, not to mention my Malware Antibytes. So I just did another system restore to three days ago (That is my ONLY checkpoint I have. And, when I try to open ANYTHING, it gives me this 'open with' prompt. I think my registry keys are corrupt from this stupid Spyware. How do I fully get rid of it? I read on Microsoft a way to help me, but I need to run as Administrator. How do I get on Admin mode? What should I do? Please help me! I'm so lost right now, it's very frustrating as I've been working until 3:30 AM for the past two nights trying to rid of this spyware/virus/whatever. I don't even have a bank account on this laptop or ANYTHING valuable. Should I reformat? If so, How? Thank you everyone!