Windows 7 runs fine on 2GB but obviously the more the better.
That Fry's deal sounds killer and should leave you with enough to do a decend build.
I recommend the following for the rest of the parts. You might be able to save more money by going with a smaller HDD but you'll find 500GB to be a nice amount of space to have around. My game folder on one partion is over 120GB and thats excluding my steam folder which currently only contains half the games I own on my steam account. A-DATA Gaming Series 2GB DDR3 1600
$54SAPPHIRE 100245HDMI Radeon HD 4850 512MB
$95 - $15 rebateSAMSUNG Spinpoint F3 HD502HJ 500GB
$55Sony Optiarc Black DVD Drive
$22OCZ ModXStream Pro OCZ500MXSP 500W PSU & COOLER MASTER Centurion 5 case Combo
$99 - $35 rebate
All totals to roughly $325 or $275 after rebates.
The 4850 should have no trouble dealing with WoW even on very high settings. And you can always add another 2GB stick down the track when you can afford it.