Repairing the install of windows is probably the best solution, as mentioned above.
However, if you have files on the drive that really are important to you, then I would recommend the following :
Before doing the repair :
1. Take drive out of machine & install it in the system you are currently using. Make sure you set it as a slave in the working system so that it boots from the working drive.
(This will work providing that current system is also XP or knackered drive isn't NTFS formatted.)
2. Make sure both drives are detected in Bios
3. Boot to windows in SAFE MODE
4. copy ONLY your own data etc from the knackered drive to the working (C
5. Switch off machine & return the drive to it's original PC (remember to set it back to master)
6. Now, boot from XP CD & carry out the repair install.
This way, if during the repair everything goes tits up, your work etc will be safe on the other machine