unfucking a computer, or ask lazy infected lj

So, I have a family member who got what's either a valid antivirus warning or a fake antivirus warning. I suggested shutting down the computer until I can get over there to deal with it.

What's the current set of good solutions for unfucking a computer? I'd like to be able to go over there with a usb drive full of antivirus/antispyware programs in case I need them.

ETA: It's a windows box. I forget what version. Vista, maybe? Might still be XP.

It's ... it's beautiful. And evil.

Via solarbird's recent post, this is delightfully evil - suggestions for evil things to commit just before a big code commit (the comments are actually readable and amusing, too)

Examples:

#define struct union
#define if while
#define true ((rand()&15)!=15)
#define if(x) if ((x) && (rand() < RAND_MAX * 0.99))