How much can you spend on the video card? If you can get a 6800 Ultra, thats a really, really good card. If you're in the $200 range, a 6600GT would also be awesome. Thats what I'm getting.
I don't know anything about DDR2 so I'm not going to say anything.
As for a CPU cooler, any simple cooler will do unless you're overclocking like mad. I personally got this one, it's a Zalman CNPS7000B-Cu.
http://www.newegg.com/app/ViewProductDe ... 119&depa=0
There is also this one, with a bigger fan.
http://www.newegg.com/app/ViewProductDe ... 115&depa=0
Very quiet coolers.