Windows

Boot into safe mode and then scan with AV

That's the problem though - I can't boot into Safe Mode...I can't reboot at all, just loops...

try scanning AV from a boot disk,
Try running a repair with the XP cd

Do you have access to another computer with current spyware, av and ad scanners? If so, pull out the offending drive, set it to slave, insert it into the second computer and scan the offending drive these 3 scanners.

While in the second computer, you might also want to save any info you really need to a folder on that computer.

When you reinsert the drive into the original machine, hopefully you will be able to at least use the original XP cd to either repair or reinstall the OS.

If the above doesn't work (and you do have access to another PC) back up all the data you want to keep. With the other PC delete and recreate the partition(s) to the way it was before the partition software and reformat the drive. Use your .ISO backup to restore to the formatted drive and try it again.

If you can't boot to anything,HD,CD or floppy, then your computer is toast. You can try putting your drive in a second machine to as others have stated, but be careful to do a full scan first so you don't transfer the problem to the new computer. If you can boot the second computer from a Bart PE CD you'll be safer.

did you get a fix for your sasser? i'm in the same boat and so far have no fix.

i thought i would see if i could get an anwer from greglanger. i didn't know it would post here