Nice system, but the asus is a little over kill if its for lan games. Maybe try using a K7S5A Pro from new egg (retail is $47 shipped) and maybe using that extra cash for some monitors, and to maybe up the 9600's to 9800's...
Also look into getting your cases from ebay, since they dont have to look good, you could get cases there for no more than $20 shipped. This would also save you a bundle of cash. And if you buy cases without locks, its very easy to make your own with a 1/2" drill bit and cable bike lock.
Even better, you can drop the 2 sticks of 256ddr, and go for 1 single stick of 512ddr from crucial at a cheaper price. Why use up 2 slots when you can use one and save the other for a upgrade down the road
And one final thing. You dont need DVD drives really. You can drop to a 52x CD-ROM Drive from lite-on for about half the cost. Which leaves more cash for the other essential parts
Truckie
PS: Good idea man...I was thinking of doing the same thing your planning. The mall wanted to much rent to do it though

I'd suggest a cost of $5.00/hour which is pretty fair considering the amount of cash it takes to set-up/build/and maintain those machines.
Good Luck!