tri-booting

okay so i've got a 20'' imac running tiger and xp (via bootcamp). what i was wondering is if there is a way that i can add another partition to so that i can also install vista. i'm trying not to delete my xp partition because i have alot of stuff on it and i'm just too lazy to back it all up. i'm probably not going to stick with vista, but i just want to try it out.. also if i absolutely had to erase xp partition i might consider it, but i want to make sure that i can tri-boot my mac first. i've spent a little time on the forums and everyone that inquires about tri-booting is asking about mac,xp, and unbuntu so if this question has already been asked, sorry i just couldn't find an answer here or on google. thanks in advance