Your Psu link isn't working but Power requirements are low with the 8600 GT needing a 300W PSU and 8600 GTS asking for a 350W. In SLI the recommendations step up a bit with a pair of 8600 GT's at 350W and 8600 GTS at 450W.
I would recomment 350W or more for your setup .
edit. Looks like that 300w-er should have sufficient amperage, but the brand and 25.99 local pizza shop large loaded with extra sauce and cheese price tag makes me weary along with the max wattage. To be safe, you should step it up to at least 400w and 24 or more +12v rail amps (combined).
Get a quality power supply with around 350-400w ratings, a lower wattage quality PSU will be a much better choice then a low quality higher watt power supply. The Antec Earthwatts 380W(27A total on the +12v lines) is only $30 after mail-in-rebate, $60 before and the SeaSonic 400ES(30A total) is $60.
kpo6969, not to doubt that you know what you are talking about but you math is not adding up. 300watt@18amp would require ~17 volt line. I can't come up with an 18amp figure divided between 5v and 12v? I could be confused a bit, but I dot see it. Even if the whole 18 amps was on 12v it would only give you 216watt, which falls 84 watts short of 300. I am just not getting it.
Looking around the card will draw 100watts. Even if that is all the draw is on the 12v it will only take ~8 amps. You should be safe. If you can find a way that the lines are marked, just place the 120mm fans on that line as well.
I would also recommend that you buy a different power supply. This one was used to bait you so to say. Even if it was still a combine 12v line it would only be 32 amp, it is only a safety thing to split the line at grater than that. There is no real benefit from a dual rail power supply. I can provide proof for this if you would like, but right now I don't have it on hand. (I am on my laptop, the link is on my desktop.)
I would also recommend the same card as kpo6969. It is a good overclock. It is also hard to go wrong with a Zalman. If you are looking to do some high res gaming, you may also want to consider this one http://www.zipzoomfly.com/jsp/ProductDetail.jsp?Product... it is 512MB, and unlike many of the other 512s it has DDR3, for about the same price as the Zalman cooled XFX. Although you lose the stock overclock.
It has a lot to do with the resolution you plan on using if you see any difference from the 512MB edition or not.
This is the XFX8600GT XXX (which I used to have) http://www.tigerdirect.com/applications/SearchTools/ite...
This is the minimum recommended psu (taken from above link)
Minimum System Requirements
Intel® or AMD® compatible motherboard
At least 512MB system RAM
PCI Express® compliant motherboard A minimum 300W system power supply
50MB of available hard disk space
CD-ROM or DVD-ROM drive
Microsoft® Windows® 2000, XP or Vista
VGA or DVI-I compatible monitor
I get the watts @ amperage part. You are stating that the 22amps is spread across all lines, and the total draw may not exceed that. 12 * 22 = 265, although 5 alone * 22 only = 110, the rest is split to the 3.3v line, and so on.
But I still don't see where you get 300watt @ 18 amp for the video card. Is there a mention to it someplace (manual, or website?)