My administration and myself didn't realize it was rated M (recommended for those 17+). Thank you for pointing that out. I feel bad now. I did specify on the permission slips what the game was and that it involves violence in a futuristic setting. I should have taken the extra time to actually read the box cover. I've played the game too and it didn't seem as bad as others I've heard about (GTA, etc...). I should have paid closer attention, and perhaps it will be the last time we choose this game or at least next time fully disclose the rating to parents and administration. This was an oversight, for which I feel bad about.
The Madden tournament sounds like a better alternative.
As far as using an existing network... we chose to create our own separate network so that there'd be no conflicts and no chance for students to get on the internet with X-Box live (which I don't think would work anyways). If you plug them into an existing network, you may have issues with 1) is your DHCP server ready to assign it an address, 2) will those assigned addresses be in the same subnet mask, and 3) can you access or control the assignment of either of the previous 2? I'm not a network expert, but I know if the only thing on the network is a bunch of X-box's, they will automatically assign themselves an address that makes them all work. X-Box Forums are helpful in understanding network settings...
http://forums.xbox.com/9/ShowForum.aspx