I know 2 courses of action to resolve this issue.
First is to boot to recovery mode from the install disks and get into the console. (DOS prompt) From there you can replace the system file with the system.bak file. ("copy system.bak system" once you are in that directory)
The other option is to rebuild the boot.ini file.
I've only ever done the first, (and then only on a 2k box) but I know there are instructions for how to do the second somewhere on the interweb.
"i would never use a firewall, even without a router protecting me. Firewalls are just wastes of memory."
name omitted to protect the innocent
the cake is a lie