A "Portable" 200kw Power Supply - half joking...
http://www.youtube.com/watch?v=GuPPKx_nCiA&feature=player_embedded
At least no one would be moaning about the gpu fans making too much noise.
However its not unuseuall for enthusiasts pc's to draw nearly 1kw with peripherals/monitor. A hundred+ of them and you have serious issues.
Even if everyone had lower power xbox's + lcd's you'd still be looking at min 75kw load.
With this amount of power consumption you will be dealing with very high end dangerous amounts of current.. A real electrician will be needed. - Just distributing the power safely around the room with enough sockets, is a logistical nightmare.
Each person will require a absolute minimum of 2 sockets ? 1 for psu 1 for monitor. Probabbly 3-4 to be safe. You can't have people daisy chaining multi plug adaptors off your system. So you may end up having to provide 750+ surge protected sockets. Maybe you could share a 6 socket gangway between every 2 seats.
These will need to be patched into multiple industrial circuit breakers. You cant have 1 person climbing under the table frying themself, and taking out every one else's system in the process.
The actuall networking side is comparitively easy. (still a huge amount of cables/patches/switches) Luckily a rack of switches/routers for that many are readily available 2nd hand, due to companies often upgrading)
Imo your jumping way to far into the deep end. Ramping up from a comfortable classroom size of 32 to 250 is madness, and asking for failure.