How to Reformat Windows XP Without the CD
Use the Windows XP setup files already included on your hard drive if you need to reformat and reinstallation the operating system without having access to the CD. These files reside in the i386 folder on the drive and contain all of the information you will need to repair your Windows XP installation. The procedure will take about 30 to 60 minutes.
Right click "Start" and click "Explore."
Click "Computer," "C," "Windows," and click "i386."
Double click "Winnt.exe" to launch the XP setup program.
Press "Enter" at the initial screen and press "F8" at the license screen.
Highlight your existing XP installation and press "R" to repair and reformat your XP partition back to stock settings.