here are my suggestions for some of your parts
CPU - Intel e8600 239.99 or if you want to overclock the cpu yourself and save money then get the e8500 187.99 instead
Videocard - Your best bet here would be to go for a powerful single card to which i suggest EVGA GTX 260 Core 216 SC 259.99 apparently you can also get Farcry 2 with this deal. Of course if you want to again save money (40 - 80) then the next best thing would be a MSI GTX 260 or Radeon 4850 1gb, 3 choices here:
HIS(Excellent cooling, 4850's are known to be really hot) <-- best choice of the 3
Asus(if you still want to support them, cept the fan is not as good as the HIS and isnt much cheaper, though i love the look on the box it comes in)
Sappire(30 cheaper than the other two but the stock cooler is terrible, expect your temps to hit 80 degrees)
Note however there is a noticeable dip in performance between the gtx 260 core 216 and the gtx260/radeon 4850
(These are my suggestions but if you want to stick to 512 card then you could find a 4850 512mb one for $130-150 on newegg)
Case - i always suggest an Antec 900, great airflow, optional sidefan, and also cool looking AND its only 59.99 right now at newegg!
Mobo - would depend on if you want to upgrade in the future, if you plan to get the nvidia card and plan to sli in the future then you need and sli compatible mobo, but if you get the radeon and plan to crossfire then you need a crossfire compatible mobo or you could just be a single-card type, and never choose to do sli/crossfire.
Memory - depends on your mobo, many mobo's are very touchy when it comes to memory so, best to choose your mobo first and then find a compatible memory, to which i would suggest 4gb (2x2gb) at 1066 or 800 if you want to save money
Power - id say 550w - 650w
Harddrive - shouldnt be to hard to find a 7200, just compare prices and reviews between seagate and western digital on newegg, im sure you can if a good one for $40-50