Do not need to mess with jumper. One way to do it is get into Bios when you start PC and select which device to boot first. But this is really not a good way to do it.
The best way is to use Bootmagic which come with Partition Magic. Just install and set up. Everytime PC start it give you a menu to select. Similar product: system commander.
There is other free way, but need tech knowledge. To use some OS loader or use the one with XP by editing boot.ini etc. I bet someone will give you instruction for this soon.