I suggest you go to this site click here and select the correct boot system for your computer.
Disconnect all drives except for the primary Harddrive & 1 CD drive.
Boot up from the boot disk you created and when prompted put in the XP CD.
You may need to format the harddrive first to get a sucessful load.
There is another possibility in that you may have corrupted the BIOS, if so you will need to either :
Reboot to setup and restore defaults
Remove the battery and /or clear the BIOS
Have a look at this page for more advice click here=