dualboot windows 7 windows xp

I’ve installed windows 7 ultimate (downloaded from bb) and now i want to dualboot it with xp. i’ve made a 20gb partition for xp and i’ve got xp pro sp3 (also downloaded from bb ) but wen i put the disk in and start the laptop again it gives me the option to start from the disk, but when i start from the disk nothing happens its just a black screen. does anyone know what problem this is and how i can fix it?
Answer #1
but why do you need 2 booting
Answer #2
I need to work with an program that doesn’t work on Windows 7 but only on xp and vista but vista is way to slow so i want xp as a dualboot.
Answer #3
start again by formatting both partitions and installing xp first then win 7 which is always the best option assuming you know your xp cd is good