I encountered this hideous problem fairly recently when a linux installation crashed. I'm afraid Gparted can't handle this problem unless you install a new ms-dos partition table, which means you'll effectively lose your XP. [If you've got a backup image - I formely used the excellent DriveImage SML - this may not be a problem, but I presume it is.] What worked for me was a an excellent little program called Boot-repair which you can find on a spin called Ubuntu-Security-Remix, or (smaller, about 350 MB) on its own startup disk, available at http://sourceforge.net/p/boot-repair/home/Home/
But first, just check that the Windows partitioning utility can't do the job for you! It's some time since I used Windows (smirk), but I have the feeling that it did notice - and was able to delete - a linux partition, which it would huffily describe as an Hope this helps."unidentified file system". The utility is somewhere among Administrative Tools - Disk Management.