The suggestion of reusable cups is a good one, and probably the most enviormentally friendly if the frat has the setup for cleaning and storing the cups (somewhat doubtful, if my foggy recollections from college are accurate).

Other solutions that are probably more enviormentally friendly than the "compostable" cups would be recyclable cups or paper cups.

Finding plastic cups that are a "1" or "2" and therefore recyclable in most areas is a bit tricky, but it can be done. I buy them in bulk for all my parties, and the empty cups go out with all the empty beer cans and bottles for the weekly recycling pickup.

Coated paper cups probably have the same "slow decomp in a landfill" issue as compostable plastic, but if you can find uncoated cups, they're probably faster degrading in a landfill, and potentially, recyclable.

Great looking out for the enviorment while you have your fun, though! Cheers!

It's also possible to rent real glasses from caterers. I suspect that the cost of the rental and the cost of buying cups wouldn't be all that different and even cleanup is easier. All you have to do after the party is stack the glasses in their trays - no need to wash them because the caterers use big commercial dishwashers. The caterers come and take them away and they're counted later. Yes, if glasses are missing they have to be paid for, but it's not a ton of money, because they get the glasses in bulk anyway.