|No reason why not.|
You will still have to reinstall both Windows operating systems.
XP will need you to emulate an ide drive during install or slipstream the SATA drivers into a customized install disk.
XP will require you to use a traditional MBR (Master Boot Record) so very large hard drives are out for your system disk(s) (though data disks would be fine).
XP will need to be installed first so Windows 7 install disk can create the dual boot options.
You have to be a little bit crazy to keep you from going insane.