If you're running a FAT32 partition on your XP install, you can use XOSL:
http://www.ranish.com/part/xosl.htm
It's a GUI bootmanager you can use to boot any operating system. In the case of Linux, you'd install lilo or grub to the / or /boot partition of the Linux install, then install XOSL in the MBR. You have to boot into DOS to actually install the bootloader, but from there you can do all of the configuration once you've booted into the bootmanager.
It's pretty neat-- I used it before I realized the FreeBSD Boot Manager was as simple as hitting F1-F4 to boot to the partition of choice. I use that now, because I'm running NTFS on my XP install.