to boot to DOS with windows XP you need a bootable floppy
to create one go to "My Computer" then right click the A:\ drive and select "Format" then check the "Create an MS-DOS startup-disk" option then hit start.
you can then boot to dos if you have that in the A:\ drive when you restart your pc.
P.S. someone asked how to do this back before the board blew up, and the post is gone now. better late then never