I find XP and 2000 to be about the same, and I too run XPpro but have it set to the Windows 2000 look and have disabled the Themes service.
For me though, XP is 1) just that touch faster 2) seems a little better game compatibility and performance wise 3) I have the SP1 XP disc, so I don't have to download 140meg services packs (which there are now 4 of for Windows 2000, not that you need to really install them sequentially, but still) 4) some of the minor upgrades to explorer are nice (albeit not too much different from 2000, but still nicer) 5) if you really like to much around tweaking Windows down to the last "drop", changing multiple video cards, overclocking and testing with a tonne of boots to test stability; sometimes you just get unlucky and muck up your Windows installation. For this -until I'm finished getting things just right- I leave on the XP system restore feature 

 ... saved me some time VS 2000 for sure atleast twice so far; then I turn it off once everything is running perfectly.
Only benefits to 2000 are 1) price and 2) activation ... which really isn't a problem to those with honest copies anyways; its only those with pirated versions of the software who get pissy about the activation. Honestly, XP activation took a mere 2 seconds for me, was easy as heck .. and again when I upgraded my hardware and re-installed it it took even less time to re-activate. So its really not a problem anyways 
go XP Pro if you have the $$ =) I'm lucky and got mine for MS employee discount rates hehehe