I am running Windows XP within a Parallels on my MacBook Pro. All my software work flawlessly and as fast as on a native installation, which I can only attribute to the excellent virtualisation technology in the Core Duo processor.
I considered installing Windows XP on a separate partition and using BootCamp to boot into it, but dropped the idea when I discovered Parallels. I was so impressed that I did not have to wait for the end of the trial period to purchase a licence. Parallels is one of these must-have software for the Mac.