an ATi 128-bit 1GB Card GDDR5 should work just fine along with the processor. You will be able to play a game like Mass Effect II maxed out just fine.
Make sure you have some decent RAM in your system and with your quad core 3.4ghz processor I don't see why you would have a problem with most games.
If you need some advice, look up some recommended system requirements for games that you would like to play.
Also for the install, just have your brother do it but HAVE HIM SHOW YOU.
I use
www.pricewatch.com for my parts.
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While on the subject here is my dream computer.
MotherBoard - Asus Rampage III Extreme $359.99 (Free Shipping)
Processor - Intel Core i7-980X Extreme Edition $799.00 (Free Shipping)
Power Supply - CORSAIR CMPSU-750TX 750W ATX12V / EPS12V SLI Ready CrossFire Ready
80 PLUS Certified Active PFC Compatible $109.99 (Free Shipping)
Video Card - Sapphire Radeon HD5970 2GB DDR5
2DVI/Mini-DisplayPort PCI-Express Video Card CrossfireX
That's what I have so far.
Anyway hope I helped, I'm off to bed i'm fucking tired.