XP will not install in dual boot

I have vista ultimate 64bit currently installed on my system, but with only 1 gb of ram really kills frames in a ot of games, so i decided to run a dual boot without bothering a fresh install of vista. I partitioned my hdd and got my 64bit XP disc loaded up. After a few minutes of formating the newly partitioned space and the proccess of copying install files on to my hdd the install prompted me to restart the computer, did so and the system booted up fine. This is where the problem reveals itself. Before getting to the install (still in DOS) the system asks me if i want to boot from cd, if i dont after a few seconds some green bits (size of a letter in DOS) pops out some times with numbers or letters on them and the computer just hangs. If i booted from CD I would go back to square one, copying installation files to my partition. I then thought to myself, okay i'll just boot back to vista, however i wasnt able to boot back to vista again, i believed XP has an older bootloader and would not recognize vista's presence. I dont have my vista disc with me atm so i cant use it to repair the bootloader... :cry

any suggestions on what i shud do?