From what I've found so far, and if it is a boot sector virus, it may have come from something like a floppy that was in you PC when you next booted up.

If you had a disk in which contained the virus, norton may not have detected it and of course now you can't get access to your drive so right now Norton isn't much help.

If you have your Windows 200 installation disks, try using these to boot your system and then enter the recovery console. When your there type either: FIXBOOT or FIXMBR, hopefully this will fix the problem.

Regard

Martin