What exactly do you mean "past the Windows stage?" What's the very last thing that you see?
If it ever gets out of the BIOS and into trying to boot Windows, there are two things that you could try. First, press F8 as the Windows part of the boot starts, and select Safe Mode. Second, put your Windows XP disc in the CD/DVD drive, boot from it, and do a Repair install.
But it really depends on how far you get and the last thing that you see on the screen. Also, do you have a system backup? If not, perhaps you should do one before playing with the system any further, to make sure that you don't lose anything. There are many backup utilities that can boot from a CD or a USB stick, so that you can backup to an external drive even if the system won't boot.