1) Bought Antec 900 case with antec trio 550 w ps.
2) Bought Intel core 2 duo 6400
3) want to buy GA-P35-DS3P mother board. ---
4) which memory 2 GB 800 MhZ is good for above MB.
5) Which video card is good -- I am not a gamer -- need it for multimedia purpose
6) which HD is good for raid setup in above MB. 320 GB--500 GB
Another vote for 8600GT. 8500GT if money is tight.
Disks: Seagate 7200.10 500 GB or WD5000AAKS (Wester Digital Caviar 500 GB) have great performance and price/GB.
If you don't have any FireWire devices (camera, etc.) look at the GA-P35-DS3R too, it's cheaper and it has 3 PCI slots instead of 2.
(Or get a GA-P35-DS3R and a PCI card to provide FireWire, if you want).