Wow that system would totally own, it sounds like your friend has a huge budget. I think the 4 gigs or RAM are overkill though, 2 gigs are standard right now.... Yes the e6400 you said he was looking at would work with the mobo, but for a little less he could buy the e6300 or e4300 and just overclock it even past the e6400... I believe they even have the same amount of L2 cache at 2 megs shared right?
Yes, they are almost the same CPU and in the end the extra multiplier doesn't add that much extra power. Going back to the RAM...unless if he has very high demanding programs 4 gigs is almost always overkill. 2 is the standard today for gaming and most apps.
I think like two 4.3ghz P4's stock. Don't worry about how fast comparrision to P4's. These core 2's kill ANY Old Single and they destroy the other Dual Cores out right now. They are very fast and will do everything you need to.
A 7300gt is quite outdated card but not the worst. You can pick those up for around 80 bucks these days. It's still not too bad of a card but yea there are still a lot better out there.