@Sealtm2 : If you want to remain in the Windows world, your choice will be fairly limited : XP64 or Vista 64.
If you're not really interested I would say, XP64 is probably the best choice (it's a very stable OS, very similar to XP but in fact based on 2003 Server. You don't have more service running than on a standard XP and you can deactivate those you don't need as easily. Personally, I will stick with it as long as possible).
The only inconvenient you might encounter with XP 64 is the fact that some hardware won't work and no one will bother writing drivers for them (it, not a concern with current hardware since all new hardware come with an XP64 driver, it shouldn't be a concern with future hardware either, at least for a couple of years but it will wastly depends on the success of Vista) XP 64 is not a mainstream OS and some company just don't bother writing drivers for it (I had this problem with a Canon 3200 scanner for exemple) This will probably not be the case with Vista since it will be the main Windows OS for a while
To sum up : my OS of choice XP 64 but knowing there might be some driver problem in the future if Vista is very successful and if the hardware manufacturers start to think making XP 64 drivers isn't worth the money

Ab