Here, try this on for size. I didn't add any mice/keyboard/monitors
the cards are dx10 compatible if you wanted to do vista, run 2 of those hd's in raid 0 for quick performance, and use the third for backup since raid 0 isn't exactly what i'd call fault tolerant. If you wanted to go really big, you could grab 2 more of those hd's and go for a raid 5 array to maximize your data efficiency and save on the spin life of the hd's. I didn't pick a tower because they're really a personal preference. As long as you get one that will house all of your equipment and is atx compatible you're good to go in my opinion.
Also, ati and nvidia are the manufacturers of the cards, geforce and radeon are the names of the cards they sell. For the most part, you can't buy a card from the manufacturer directly. 3rd party companies purchase the cards in bulk and re-package and distribute them individually. I chose evga for the graphics cards, and evga distributes the geforce card i like.
The speakers are out of stock but you can get a nice bose surround sound system with the extra cash, or spend it on safeguards:
i.e: power-stirp, UPS, Exhaust Fan, Water cooling, additional fans, software, etc...