First off, you'll have no problems with any of those operating systems recognizing and using 2GB of ram... well with the exception of course of WIN95 haha!
Anyways... 2000 works great for a workstation system, but for a home computer, you'll be best off with XP.
The question is.. do you want to blow your only copy of XPPro on this or not. It's really up to what you're going to use this computer for.
If you're just wanting something to surf and play on, XPHome should do the job nicely for you. Also XPHome supports up to 2 processors, and your X2 will appear to be just that.
If you plan on using a RAID setup, or plan on using the computer for advanced reasons, especially if you'll be using it with work as well... then go for the XPPro.
But any of them will function just fine with your hardware.