brief 5-box 1-PC guide

quad core processor (intel preferred but NOT necessary, WoW is old)
mid-market or better video card, older generations fine, double-decker cards can have issues (does not need to handle Crysis at max, but does need to handle several 3d apps simultaneously)
8GB+ RAM with any reputable brand at all standing behind it
SOLID power supply, Corsair is good, others if you research it well (very well, most people don't know good PSUs from bad until it fries their computer, and many of them write reviews)
7200 RPM hard drive with enough space to install WoW (IMO messing with RAID is too much trouble if that's where you were going with 2x320GB, but low-budget SSDs can be helpful for some things)
as many pixels as you have money for with as good of a panel as you have money for
something with keys
something with buttons
something that beeps
something that can read WoW install discs
something to plug a network cable into

Starter questions: can you install anything yourself? Something as simple as connecting a hard drive or installing memory can save you money. 8GB of memory doesn't cost that much these days...but more if you get it preinstalled.