How do you reinstall windows XP without the original XP installation CD?

Test the CD by inserting it into the drive and rebooting your PC. As long as the CD is earlier in the PC's boot order, the CD will take over the boot process and go into it's restoration routine. Depending on the manufacturer, this may be a complete rewrite of the hard drive, or a choice to only replace the Windows files only. This is important as a complete rewrite will overwrite your personal files and added applications too. If no choice for "Windows only" exists, you need to exit this restore process and find a way to get your personal (My Documents, email, Quicken data etc...) files off this PC, and then run the CD boot restore again. After it is restored, you can copy your data back again. If you do not need your personal files or have a copy already, you can proceed with the overwrite. Remember to do updates for Windows and apply all Service Packs for Windows and other MS applications.