First, its a good idea to take a backup of your personal files.
Then insert your windows xp install cd and shutdown your computer.
When you switch it on again, it will boot from the cd, and go into the recovery console; it will ask for the admin password.
Then in the DOS prompt type “fixmbr”.
After you’ve fixed the MBR, shutdown your system and switch it on again. It should boot into win xp.
You can then go over to the control panel, and in Disk Management delete the linux partitions and create new NTFS partitions. You may restart your system finally.