A Radeon HD4850X2 (single card, two HD4850s) performs well enough for $280-300 USD. For motherboard, I've heard good things about the Intel DX58SO. A friend of mine just got his second X58 board and is awaiting his 3rd--he first bought the DX58SO, he just got 2 days ago a Biostar TPower II X58, and is expecting a DFI X58 board.
http://www.newegg.ca/Product/Product.aspx?...N82E16814102809I just looked your HDD up on Seagate's site--it may be effected and frankly thus dangerous to run. As I said, there's about a 40% defective rate, so I'd say just skip it and buy a different drive. In retrospect, my WD Black 1TB drive is the fastest of my three drives.
Western Digital Caviar 80GB:

Western Digital Caviar SE16 (the old 2-platter version) 320GB:

Western Digital Caviar Black 1TB:

I'd recommend the WD Caviar SE16 640GB instead.
http://www.newegg.ca/Product/Product.aspx?...N82E16822136218On a side note, I do have this forum post about it...
http://www.jonnyguru.com/forums/showpost.p...amp;postcount=1I doubt they'll be free from shelves in the next few weeks, so the WD CavSE16 or WD Cav Black 640GB drives are better choices.