Glen, I don't know much about O.S.s but bought a computer for work the other day and read about Vista vs. XP professional on the website of a company that make the demanding seismic reflection interpretation software that I use. It said the XP prof. is faster but Vista is more secure. It also said that several flavors of Vista are not good enough for the new versions of their software...needed business or ultimate or something like that.
I got XP professional 64 bit, and computer had 64 bit intel core duo.

oh, yeah..search around in support or something at www.seimicmicro.com for their O.S. advice but probably not very applicable to you.

I lust after Apple Mac air though...the commercials make it look really nice...but it probably is missing things I need (DVD reader?) and I don't want to mix operating systems: am going to keep using the 2 computer route: clunky desktop replacement at HW's lab, and the new lighter, less energy guzzling one for home and travel.

Chris