I don't know anything about xp but if fancypiper's hint is not to your liking
then grub comes to the rescue thru typing a few commands and pressing the enter button for each line.
You have what I call the grub acting like a bash command line interface or in windows speak like a DOS command line.
post your xp partition info like all of it is on the first drive first partiion or I have a vm partition as the second partition etc
in the mean time here is a link and its booting info
for the manual
and here are commands (and press enter ) for first drive first partition
grub> unhide (hd0,0)
grub> rootnoverify (hd0,0)
grub> chainloader +1