Don't sweat it Rosco, you still have at least a year before it happens.
Oh, and it also will not work on Windows 2000 either. You'll be able to update XP so it can run (install all the .NET stuff).
It will be instersting to see what happens to OpenGL, as it is going to need a major overhaul when Longhorn hits. The jury is still out on this.
Of course, MS could change thier minds about all of this. Longhorn has been revamped at least twice so far. The first iteration would not run on most computers due to the overhead for the desktop (required at least an ATI 9800Pro or faster video card just for the desktop), the second iteration is better, but it still is not final.