Personally, I prefer XP.. it's very stable, highly customizable, and quite secure. However, if Win2k is doing what you want it to do (ie. not crashing), don't bother upgrading.
You know the saying: "if it aint broke, etc..."
As for Home Edition vs. Pro: Decide for yourself.. it all depends on what features are important to you..
There's a handy comparison
at microsoft.com that might help you decide... also keep in mind that Pro costs substantially more than home (you were planning on PAYING for it, weren't you