If you plan to game, get as much RAM as possible (at least 2GB, 4 if you can swing the cost), a good video card and the fastest processor you can afford.
Remember that DUAL CORE CPUs don't necessarily make games run faster, but they DO allow you to do multitasking things like burn a DVD while playing a game (one processor runs the game and the other handles the burning task). If you don't think this will be an issue, you can get a very fast single core CPU for less money than a slower dual-core - it's all about what you need the PC to do.
ALso, don't bother with a sound card as most MOBOs have 6.1 right on the board now, and re-use your HDD, DVD, CD and other optical drives to save cost. You can even recycle the case to save $40-$100 if you're not sick of looking at it.
I'd part everyhtig out at NewEgg since their return policy is well-known to be A-1 and everything there has Extended Parts Warranties for only a few bucks per componant.