nope - you need to install XP directly onto your bootcamp partition. You cannot use your parallels installation. You CAN, however, do it the other way around - install XP on bootcamp then create a parallels VM that pulls from it.
For reasons I can't even remember, I installed my Boot Camp XP on an NTFS partition; can Parallels still use that installation? If so, I'm going to wipe my Parallels "machine" and start fresh to save a few GB of HDD space.
You never needed to licenses. When you go to install the second time (say, Parallels after you've already used the disk for Boot Camp) you just have to call the 800#, speak to someone in India/Pakistan/whatever for ten minutes, and they'll give you the key to unlock it again.
I flat out told them that I was installing it as both a virtual machine in Mac OS X and to dual-boot on the same computer, and they gave me the code straight away.