.........is it posible to put Windows Vista or the Apple operating system onto an external hardrive and run it on a Laptop that has XP on..........Thanks

Yes, look here.

ive never done it but i imagine that if you can boot from usb or cd etc and install the necessary drivers for the external drive then yeah. why not?

Yes, set your bios to boot from CD then, USB hard disk, install the OS to there and set up a boot manager to allow you to pick the local OS (Default) or manually select the OS from a CD drive.

HTH