Virus is killing my desktop!!!!EMERGENCY

Info:
Dell Desktop running WINXP
Virus warnings begin popping up from a program that are NOT my anti-virus program. I try to run MY anti-virus, AVG free, but it won't open.
I try to run Spyware Blaster, but it won't open. All the keeps popping up is the FAKE security program.
Other windows start popping up, all **** related!!!
I BUY the upgrade for AVG and download it. I can't find it anywhere on the computer.
I can't open computer in Safemode
When I boot the computer - I get the Windows logo screen>I get the users screen> I click on users screen and my desktop opens SLOWLY>my pic on my desktop is missing, there's only a grey screen. Any icon I choose activates the FAKE anti-virus program and warning windows start popping up until the **** windows start popping up. Today the FAKE anti-virus program popping up is not the same one that was originally popping up.
HELPPPPP!!!!