I have done exactly what you are thinking about with Windows XP and Parallels.
I used bootcamp to do a clean install of Windows XP and then configured Parallels to use the bootcamp partition. I have not had any problems to date and everything does work smoothly. Could either boot up with Windows XP or just start a virtual session from Parallels. Everything picks up exactly from the last palce it was left no matter how you had used XP last.
I had tried Fusion when it was in beta mode, but somehow I liked the interface and easy usage of Parallels compared to VmWare. Maybe it was just the first mover advantage Parallels had and it had me hooked and I never bothered to use VmWare again as Parallels just does everything I want without any problems.