probably a dumb question....

i just got RH9 and i installed it on my newly formatted hard drive... it installed grub and booted fine. then i installed windows xp and it overtook the bootup and i can no longer boot into linux. both os are on the same drive but seperate partitions. i tried changing the linux boot partition to active but that just caused a error and didnt boot at all. anyone know how to get my grub back???? or posibly set up xp so it will give me a boot menu????
thanks..