My New Build (First Time Builder) - Looking for Input

Ok, so I am planning on finally building a new rig. What my goal is, is to have an economical gaming rig. Below I have listed my components. I put a lot of thought into it and just wanted to make sure everything, at least in theory, is compadible. The computer came out to $729.92. That's without including rebates and only including new egg prices....but it also didn't include shipping. So, after rebates and really shopping around for the best deals, it shouldnt cost me more than $700. Anyway, here is the list:

Intel Core 2 Quad Q6600 2.4GHz (Not trying to go for top notch CPU, just as long as its a quad core...I can OC it later if I feel the need to)
http://www.newegg.com/Product/Prod [...] 6819115017

GIGABYTE GA-P35-S3G LGA 775 Intel P35 ATX Intel Motherboard (I like this board because the price, reveiws, gigabit ethernet, decent built in sound, 5 PCIs, plenty of ports for my uses)
http://www.newegg.com/Product/Prod [...] 6813128084

SAMSUNG Black 22X DVD+R 8X DVD+RW 16X DVD+R DL 22X DVD-R 6X DVD-RW 12X DVD-RAM 16X DVD-ROM 48X CD-R 32X CD-RW 48X CD-ROM 2MB Cache SATA 22X DVD Burner
http://www.newegg.com/Product/Prod [...] 6827151171

Western Digital Caviar SE16 WD2500AAKS 250GB 7200 RPM 16MB Cache SATA 3.0Gb/s Hard Drive (I like WD, nice size cache, good price)
http://www.newegg.com/Product/Prod [...] 6822136161

SAPPHIRE 100242L Radeon HD 4850 512MB 256-bit GDDR3 PCI Express 2.0 x16 HDCP Ready CrossFire Supported Video Card (awesome for the price, and beats out similar NVIDIA cards in the same price range)
http://www.newegg.com/Product/Prod [...] 6814102747

OCZ Platinum 4GB (2 x 2GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel Kit Desktop Memory (first choice was Corsair XMS, but these were much cheaper and reveiws were pretty good)
http://www.newegg.com/Product/Prod [...] 6820227298

Sunbeam PSU-HUSH680-US-BL 680W ATX 12V 2.0 Power Supply (nice PSU, but not sure if it is enough wattage...in the future I may experiment with overclocking and also a RAID 0 configuration, so that is something to take into consideration)
http://www.newegg.com/Product/Prod [...] 6817709015

LOGISYS Computer Area 51 CS51WBK Black Steel ATX Mid Tower Computer Case (seems like an ok case for the money, plus it comes with a 450 PSU...dunno, maybe someone could suggest a better one)
http://www.newegg.com/Product/Prod [...] 6811148030

Putting VISTA Ultimate 64-bit in it (how much of a decrease in performance will I see between ultimate 64 and home premium 64? Only reason i am going with ultimate is because I can get it for free, or else i wouldn't even touch it)

do you plan to crossfire in the future?

No, I dont plan on using crossfire, with this rig at least. And about the PSU. Yes the came comes with one, but the one it comes with does not put out adequate wattage...so I would just take that out and sell it on ebay. There are other cases of equivalent price, but didn't come with PSUs, so I figured I would go with the one that has the PSU.

But yes, I figured somone would say that I should invest in a nicer case, and I do agree. As for the PSU, I will check out better brands, but is the wattage ok for my build?