Only buy an AM3+ motherboard , preferably with a 970 or 990 series chipset so you can upgrade later .
Consider the FX 4100 rather than the phenom . Its cheaper and overclocks well [ when you change your mind] but till then its performance is comparable
The RAM should be 1.5 volt or less , but dont buy 4 x 1 gig sticks . Get 2 x2 gig , preferably 1600 MHz
You will not need the powere of a 6950 at that resolution . A 6870 or GTX 560 [ not the TI] will play anything on the highest settings
The Antec 300 Illusion is an excellent case and was only $40 when I last looked
are u sure that a gtx 560 will perform best for games like bf3 at 1600x900 and future games after 3-4 years not at that res but some what lower like 1333x768 minimum res with high settings..if i buy a gtx 560 i will invest the remaining money in i5 2400 with an intel board dh67vr(cheap amd most reliable with usb 3) and about ram any h67 board supports only 1333mhz