First, you'll need to free up some space and create a partition for your RH8 install (I'd download RH9, its out now). When you install RH, it will give you the chance to setup your boot menu; just properly identify your XP partition during install, and all will be happy. Alternatively, you can read about GRUB, a bootloader shipped with many modern Linux distros. Read about grub at http://www.gnu.org/software/grub/.

-C