Well, I would definitely go for the Intel setup. The Core2Duo's put the Athlon 64's to shame. The E6400 is a nice processor, but if you have the extra money, go for the E6600. It's supposedly amazing, and also has been reported to have been overclocked to 4.0 GHz on only air cooling (no water cooling, from 2.4 GHz. That's a 66% overclock!).
As for the motherboard, if you're going for value, that is a great one. The only thing is that if you are planning on overclocking a lot, it sounds like this motherboard gets pretty hot. But for the value, you can't really go wrong. If you want to do some heavy overclocking though, spend a few more bucks and get the Asus P5B-E:
That memory seems good, the only thing I would think about is that since it's not really a well known brand, you won't know how well it's gonna overclock until you actually test it. Eventually, you may also want to add another 1 GB of RAM, but I would wait until you save up more money.
If you do a lot of gaming, you may want to consider upgrading your graphics card. What do you have right now?
I bet you can probably get around $100 for those parts.