I think this is the first time I see this problem
Mint has not changed the title I think.
How much do you know about grub?
You see, when you install Mint "the normal" way it's the grub, and thus menu.lst, of Mint that is in control - no matter what you do to the grub of Ubuntu - no change.
As you can boot check the content of menu.lst in Mint
It should have valid entries for both XP and Ubuntu
To me it seems that you've been looking in the menu.lst of Ubuntu
If that's not it....
The entry for ubuntu should be as you have it, but replace the UUID with /dev/sda2
the entry for Mint should be
title Linux Mint, kernel 2.6.22-14-generic
kernel /boot/vmlinuz-2.6.22-14-generic root=/dev/sda6 ro quiet splash
As you see the same except that Mint has exchanged UUID for /dev due to the massive amount of problems with UUID