There's a lot to consider here. If you plan on going with Vista, you'll be better off with this version :
http://www.newegg.com/Product/Produc...82E16832116205 The 64 bit version allows for more memory than the standard 3Gb's that 32 bit support. It allows for future expansion, and is the same price.
Also, are you planning on using Crossfire or SLI graphics? As the standard recommendation is to use at a 1000watt psu.
For your memory, I would recommend this :
http://www.newegg.com/Product/Produc...82E16820145043 Because of quality, Corsair, OCZ, and Mushkin are your best buys.
I do realise you are on a definite budget, but try not skimp on components, since most of my problems in the past were due to settling for the cheaper parts, but they also can cause more problems since their quality isn't up there.
Because heat from all those high powered parts is a grave concern, you may want to think about something like this :
http://www.newegg.com/Product/Produc...82E16811129021 It comes with 4 fans in it already, including a big 200mm exhaust fan out the top of the case towards the back. If you opt for the other one, be ready to modify and add fans, and or a water cooling system to keep those parts down on temperature. Also, from my own experience, AMD / ATI components tend to run a little warmer than Intel and Nvidia, at stock settings. So, if you wish not to have potential heat issues, you may wish to consider something a little robust for cooling purposes.
But do research it a bit more thoroughly though.
Hope this helps!