Please help with new PC config

Hello all,

I'm looking for some advice as to how to best put together my next PC. Bought my last pc about 4 years ago and had a lot of grandiose ideas of what I'd be using it for - which never really panned out - so I think I wasted a lot of money by going crazy with the check-boxes on the config page. This time I'm trying to be more realistic. I'm looking for a rig that will basically play World of Warcraft (and its expansions) at top settings (My monitor only supports 1600x1200, I believe, though) without hang-ups. I've given up hopes of a super pc that I'll handle my TV, gaming, and home cooking with, and just want something that I can game with for the next few years w/o worrying too much about upgrades.

I have a couple specific questions: Dual vs. Quad core, XP vs. Vista (32 vs 64), Ram (2 vs 4Gb vs more), Liquid vs. Air, HDD - 10k RPM that important?, And which video card do I realistically need to run WoW at max settings for the next few years? Ok, so more than a couple specific questions..

I consider myself somewhat mid-range in my build-it-yourself know-how.. But I'm probably overestimating my skill. I'd definately feel less confident putting together liquid cooling than air, since I've never done that. However, I work 80+ hours a week in a hospital and don't have a lot of time for trial-and-error of building from scratch - so - how much time investment does it realistically take to put a pc together from parts? Should I just suck it up and pay extra to let some company put it together and send it to me two months later?

Budget-wise I'm by no means rich, but I could hit $1500 or so before I start getting too jumpy.

Sorry for the wall of text, but I'm excited about getting a new PC, yet really don't want to spend extra $$ on something if I'm never going to notice the difference. Any help would be much appreciated.

Thanks!