Ok, based on the requirements of wanting a decently Wow-capable PC for under $500 I quickly spec'd out the following:

CPU Core 2 E4500 118.99 http://www.newegg.com/Product/Produc...82E16819115031
MoBo Open Box Intel 44.99 http://www.newegg.com/Product/Produc...2E16813121323R
RAM 2gb Crucial ballistix 54.99 http://www.newegg.com/Product/Produc...82E16820146565
Video EVGA 8600GT 79.99 http://www.newegg.com/Product/Produc...82E16814130085
HD WD 120GB SATA 44.99 http://www.newegg.com/Product/Produc...82E16822136225
Case 500W MicroATX 89.99 http://www.newegg.com/Product/Produc...82E16811144138
433.94

This is all using name brand parts that aren't exceptional, but are certainly capable. You could save additional money by buying generics. No peripherals or software is spec'd. I'm not sure about the quality of the case, but other than that this spec should run Wow quite well, and leaves your wife some shoe money.