Back on topic, Vista is the latest version of Windows. Generally people prefer it. Techie types don't, in the same way that those people hated XP when that came out. Techie types usually don't like change.
Vista v XP depends on the hardware. Core 2 Quad, defo Vista, due to old licencing restrictions on processor numbers. Any Core 2, I'd say Vista, due to its ability to better support the processor. Lesser processors, such as all AMD and P4, more difficult to call. Seeing as nobody is going to put much effort in to XP now, seems pointless buy new with XP.
However, if your computer is low on hardware spec, XP may well run better (though XP SP2 has huge performance issues, alledgedly fixed in SP3). Vista really needs a minimum of 1G, ideally 2G. Memory so cheap, not an issue. If you want the Aero desktop, a recent discrete video chip, or a current generation integrated.
I recently paid £450 for a 2G Core 2 Duo, 965 chipset with X3100 video, 1G RAM, 160G HDD, DVD+-RW/RAM, which runs Vista Business. Works very well for non gaming apps, though I am getting more memory (£35 for 2 x 1G from crucial, throw away the 1 x 1G factory fitted).