Firstly let me say most of my Linux experience is with Suse (ver 9 and 10)and I assume Linux was installed after XP
In Linux go to boot loader config. there you should be able to find an option of restoring MBR. Then it should be safe to wipe off the Linux instalation.
Or alternatively Grub can be written to a floppy so it still works even after Linux has gone.
Or you can use XP repair function "fixmbr" to rewrite the master boot record
At different times and for different reasons I have successfully used all these methods but I am no expert and might just have been lucky!