There are at least TWO PLACES that I can cause "Professional" to display. One is the BOOT.INI boot menu and one can edit that to say "Fifty foot dragon tail" or anything you want. The second common area is a splash screen. It's best to not diddle with that.
What I'd like to know is why the word "Professional" went away at start-up and I'm runing WinXP-Pro on my system. I have checked the properties & it still says WinXP-Pro & my serial number for Pro.