I think you did very well Nazna. Few things I'd point out or do differently...
Phenom II X4 3.2 GHz Quad Core - Great price and a good CPU. Invest $40 in an aftermrket CPU cooler and overclock this to 3.8 ghz and you're set for 5 years
GeForce GTX 550 Ti - Its a good card, but you could have founda slightly better card for same money. 1GB GTX460, AMD 6850/5850 tend to hover around this price. 550 is an excellent card now but in 2 years you may have to upgrade.
Biostar mobo -Great price however I personally would have invested in a SLI capable mobo. Dual graphics cards scale really good these days. You would have to spend about 50 bucks more tho for mobo with 16X/8X dual PCIE 2.0 slots...
650w Power Supply - perfect for low/mid range SLI if you ever want to
