For this hack you must have an ISO image of a bootable Windows XP in your hard disk. Google it..
Step 1: Download the software "Unetbootin" from here.
Step 2: Run the application and specify the location of the ISO image.
Step 3: Specify the location of the USB pen drive i.e the drive letter.
Step 4: click next and wait for some time.
Now you have created a bootable pen drive. Restart your computer and boot from the USB disk and the the booting must start.
1. pen drive must be of at least 1GB capacity.
2. some computers can not boot from a USB drive so this won't work for them.