Do not buy a cheap generic wireless card for $20. Spend $40 on a good name brand model.
***That power supply is overkill for your system, you'd be fine saving some money for a 600watt... unlesss you do plan to Crossfire then it's a good pick.
However, theres no reason to crossfire if you're running games at 1440x900. It's such a low resolution, a single 5850 would be fine. (although I'd highly reccomend a GTX460 1gb instead)