JPC
Yes you can have Win7 and XP in a dual boot situation. I did it when
Win7 was in beat and didn't have any problems. Though there's just one
thing to keep in mind, and will make things a lot easier in the long
run. Install WinXP first, then Win7. But if you're buying a new pc
that has Win 7 already installed, then go by this tutorial to dual boot
with xp and 7.
http://apcmag.com/how_to_dual_boot_vista_and_xp_with_vista_installed_first__the_stepbystep_guide.htm
Although it says it's for Vista, the same steps will apply for Win7.