Here are my full system specifications:

PC Case: Antec 900
OS: Microsoft Windows 7 Home Premium Service Pack 1 32-Bit
CPU: Intel Core 2 Quad Q9400 2.66GHz
Memory: 4x1GB Corsair XMS2 DDR2 SDRAM
Motherboard: XFX nForce 750i SLI
PSU: BFG 650W SLI
GPU: BFG GeForce 8800GT
Sound Card: Creative X-Fi SoundBlaster XtremeGamer
Network Card: Linksys Network Adapter Card
Disc Drive: HP LIghtscribe DVD+-RW Super-Multi Drive
Hard Drive: Western Digital 750GB SATA

Here are the websites that describe all of the features of my pc case (http://www.antec.com/Believe_it/product.php?id=MjM=), my power supply(http://www.newegg.com/Product/Product.aspx?Item=N82E16817702003), & the graphics card that I am looking at(http://www.newegg.com/Product/Product.aspx?Item=N82E16814121429). I used the power supply calculators on Newegg.com(http://educations.newegg.com/tool/psucalc/index.html) and Thermaltake(http://www.thermaltake.outervision.com/power). Newegg.com suggested that I needed 691w of power and thermaltake suggested that I needed between 750w and 818w of power. I looked at a few forums about whether 650w power supplies could support a gtx 580, some said yes it could and some said no it could not, but I’m still not exactly sure whether or not my current power supply can handle everything that I plan on adding to my pc or should I just upgrade to a power supply with more watts just to be on the safe side. If I should, what would be a good brand to get? I have been looking at ones made by Antec, Corsair, Cooler Master, Kingwin, & Thermaltake.

Thanks!

I have the Antec 900 myself…I know the new graphic card will fit..but it’s going to be a tight one. Power supply-wise, I would recommend you to get a new one. 750W is the lowest you can start.

Past three systems I’ve built…two power supplies are from Corsair and last one was from Antec. they’re both great PS manufacturers. What made me switched to Corsair was stability when overclocking my system and quietness. However all the one you mention are good, keep in mind you do have to pay more on the higher end Power Supply.

Take a look at Corsair AX850 or AX1200

http://www.microcenter.com/single_product_results.phtml?product_id=0378290

of course after i change the power supply

Here is another question on Yahoo answers similar to yours.

http://answers.yahoo.com/question/index?qid=20110715005336AAqW1FP

The guy is basically asking if a intel H61 Express motherboard would work with the GTX 460 and everyone said it would.

One of the answers: "Yes. The motherboard will support the GTX460 as long as it has a PCI-e slot which it has. Unless you have a really low end motherboard that does not have a PCI-e slot, it won’t work, but the cheapest H61 boards have them so yeah."

And: "Yes, you can install the GTX460 on your M/B as it has a PCIe x16 slot for the Graphics Card.
The card will definitely work well on the "level" of your Motherboard."

So yeah it will work. Hope this helped.