My wife has bug issues, mainly lag based and has to have the setting turned down really low, but her PC is nearly 3yrs old. The one I got in March runs it like nobodys business, and it isn't a hardcore machine, budget gamer PC about £600 from a PC gaming site shop, its a dual core, with a decent card 8600 GT, with 4gb RAM.
It seems vista has more problems than xp from what I've heard, but I rejected vista when I got my new machine because I like where xp has got to.
I'm loving the game tbh, the only issue atm is most of the WoW group I went with are playing Order more, while I and my wife are liking Destruction more, but we have the two guilds set up so hopefully it'll work out.
Oh and two things I love in particular, loads of titles to pick from, silly through to cool, and the ability to take a surname at Lvl 20. So a few days ago I got Meriann Lightning on Karak Hirn, a thumbs up to anyone who knows where I got that name from.