Knanda,
Hi!
I am researching the prices or a similar configuration myself, and have been doing so for last couple of months.
Why are you chosing ATI HD 5850 instead of a nVidia GPU. I am led to believe that nVidia is a better GPU.
Also, if you are choosing a DDR3 RAM, then having 4 GB is not a good idea. DDR3 is a 'Tripple Channel' RAM and therefore you need to populate all three memory modules. I suggest buy either 3 GB (1GB per module) or take 6 GB (2 GB per module X 3). Atleast that's what I am planning.
From what I have researched, for the configuration that you are thinking of (and me as well) 600 Watts of power supply is not going to be adequate. Atleast I am looking at a minimum of 750 Watts (but prefereably 1000 Watts). That will help in making the computer 'future proof' as well (if anyone can do such a thing).
Lets keep in touch.....