Magic, sorry to hear about this. Saw your thread over at MW but wasn't sure it was you.
I don't have any experience with this, but I believe you're going to have to create & use a boot disk to get into Windows. Then you may have to install and use the Recovery Console to fix the file causing the problem. I don't know the exact instructions to give you, but can help you get started.
First I need to know if you have your XP installation CD. If so, is it a Setup CD or Recovery CD? If it says recovery on the CD I'm pretty sure that, when inserted, it will automatically reformat & reinstall Windows. I'm sure you don't want that until you've had a chance to back up your important data at least. But if we need to use Recovery Console, it has to be installed first--a setup CD is easiest, but it can be done in another way.
Either way I think you will need a boot disk. I hope whatever computer you're on has a floppy drive. Go to this link
to begin making the series of disks required for XP. Some general guidelines are HERE.
And Hone page
Basic information on Recovery Console is here.
We may not have to use it, but that will give you an idea of what is involved.
See if you can get a boot disk made & find out about the CD. And if both computers have floppy drives. Let me know how this first step goes. Good luck.