Now as for data storage, new games are increasing becoming 8 gigs after install. If you plan to use the PC as a media center also, then that is ~5 gigs per standard def. movie.
If you want the performance of a 10k rpm drive and need the storage then using the Raptor as your operating and game install drive, and purchasing a 320gig or 500gig hard drive as a slave would be best.
The 680i really isn't a bad board, when it first came out a lot of people used it and if you can get a deal on it in a bundle it would be great.
For the money, the 640mb of the 8800gts is worth it. Especially if you decide to buy a new plasma or lcd tv and want to play on it.
Like stated above, G. Skill memory is a great deal. 2 gigs is the standard right now for gaming.
Since you are buying the 8 series video card Windows Vista is what you are going to want. XP does not support dx10, that would be the main reason for building a new pc right now