Method #1:
-download Gparted (search it on google)
-burn the .iso file to CD
-restart your computer and boot from CD
-choose autoconfigure and choose language and keyboard layout
-wait until loaded
-at the top right hand corner, make sure the right hard disk is selected
-right-click the "ext3/ext4" Ubuntu partition and mark it for deletion
-do the same for the Ubuntu "swap" partition space
-click apply selected tasks (or something similar to that)
-let it do it's thing
-expand Windows XP partition, and apply
-let it do it's thing again
-when finished, restart
-the Windows XP partition WILL MOST LIKELY BE UNBOOTABLE AND/OR CORRUPT
-get your Windows XP disc and do a repair installation (if it is unbootable)
ALL STEPS DONE
Method #2:
-right click "My Computer" and click manage
-choose disk management on the left
-right-click and delete "unknown" partitions (Microsoft Windows does not recognize Linux partitions)
-when done, use gparted to expand the Windows XP partition, you cannot do it while Windows is running
ALL STEPS DONE
This can be a lengthy process!!