put in the XP CD on boot, go to the recovery console and type 'edit.com C:\boot.ini'
put this into the boot.ini:
multi(0)disk(0)rdisk(0)partition(1)\Windows="Micro soft Windows XP Professional"
then save and exit
if you cannot edit the boot.ini because it is read only, make a new one and call it a different name, put in what I posted and save it, then when you go back to the recvery console type 'copy C:\[the file you created] C:\boot.ini'
Codeine: if you haven't got your CPU already, try and get a winchester core