I keep telling people (who are apparently in denial) that XP *will be* the replacement for 2K, so you might as well learn it now. 😉
The main difference (other than the upgraded kernel) is that the interface is "skinnable". Also more bells and whistles are being integrated into XP. XP will functional on 2K drivers for alot of stuff as well. The Office Products are called "XP" too and they are being written to optimally work with XP.
The downside (which is being put in place anyway for all new M$ products), is the product activation.
[EDIT: Let me add that XP will have a "consumer", "Pro", and "Server" version (with varying types of server), and where "server" will initially be called "2002" so that all those schmoes who have suddenly found themselves obsoleted won't feel so bad 😛(but it is still XP in reality).