Completely blocked computer

Hi,

I got infected with a very bad virus. HOT SEX, Error Cleaner, Privacy Protector, Spyware&Malware Protection icons appeared on my desktop while some windows were opening/closing from nowhere. I panicked and pushed the Restart button, and from now on, 10 seconds after the computer's startup, it freezes completely; I even hear the fan/HDD inside the computer case slow down. The mouse still works, but that's all.

Even if I try to boot in safe mode, when it comes the time to choose the safe mode, the keyboard no longer responds; enter, arrows, I cannot choose the mode.

Now, I'm on my Mac (thank god Macs exist) and still searching how to get rid of this shit.

I can't even run HijackThis! : (

I have Windows XP Home, Core2Duo, 1024 RAM.


Thank you for your answers