Actually i have a rather similar system (2.4 ghz amd 64 x2 9800gt 4gigs of ram and 2 500gig hds) and i have one of these, http://www.newegg.com/Product/Product.aspx?Item=N82E168...
its kinda overkill but i got it with upgrading in mind.
I recommend that you get a least a five hundred watt or more (the first one)
xoxide is a good site and most of their stuff is on clearance right now (i got 6 12 inch cathodes for 14 bucks!!!) so you might want to get a psu from there.
eVGA recommends at least 26A combined on the 12V circuit for their 9800GT.
Some of the PSUs you were looking at are under that minimum recommendation.
The ST400 PSU offers 29A, so it should do, but it's leaving almost no room for upgrades. Also, you will not be able to reuse it in your next build, or if you upgrade the video card. If all that is acceptable, go for it.
Quality cannot be over emphasized when buying a power supply. There are many areas where you can go cheap, but the power supply should not be one of them. It makes no sense to fry your nice video card and mother board because of a $39.00 power supply. I would recommend that you look for several particular brand names at Newegg. One of them is PC Power and Cooling. Another is Corsair. These two companies do not make a bad quality product. You will pay a little more but please beleive me when I say it is worth it. I burned up an Nvidia 8800GTX video card and a Gigabyte P35 motherboard with a cheap no-name power supply. Never again. Good luck.
thanks for these excellent replies. im kinda on a budget here so i dont want to be spending more than 50+ on a power supply, but i also do not want my computer to burn up. i heard not so good things about StealthXstream and their rebate process... but i heard they also have quality products. do you have any experience with the rebate situation aevm? again, thanks for these replies.
I would like to re-emphasize what jlabit said. Quality is very important in a power supply. Corsair and PC Power and Cooling are both very good brands. Above is a link for a 500W PC Power and Cooling single rail power supply for 49.99 after mail-in rebate. They have some less expensive 410/420W supplies as well, but you'd probably want the 500W.
A cheap power supply from an off brand can be detrimental to your system, and is liable to go out of service under heavy use. Any way you look at it, you'll be probably be paying extra for it.
choosing a power supply is very difficult lol. im probably an idiot but i went with the corsair 400CX. http://www.newegg.com/Product/Product.aspx?Item=N82E168... there are soo many different power supplies to choose from. when i was thinking about buying a certain power supply, there was always another one that seemed a little bit better. having to deal with the price and the amps and the quality.. ugh. anyways have a merry christmas everyone and thanks for the replies.