Is the PC i'm building good?

Yes its fine and their is no use in going with DDR3 atm. Its still fairly new and too expensive to get. If you get 4 gigs of DDR2 Dual Channel Highspeed ram you still be doing just as fine. You can scratch the DDR3 and get a 8800gts which are only around $159.00 but the 8600gt will do just fine. But all around the computer you are building here is more than enough to run todays games. Ive built many computers like this one and ran games like crysis in high settings doing around 45fps with AA x2