Does anyone have any ideas for entertainment in Zurich? We are also interested in going to Interlaken for the day. What would be the cheapest way to get there?
The cheapest way is via train (but nothing is cheap in Switzerland). Look at www.sbb.ch/en for your rail connections. Zurich to Lauterbrunnen takes about 2.5 hours. So you really don't want to do a "daytrip" as you'll waste 5 hours sitting on a train.
And what will you do in Interlaken? It isn't in the mountains, you know?
By the way, there is a better than even chance that Zurich is the most expensive city in Switzerland. Is there a reason you are concentrating your time there?
This is effectively a duplicate of a question in Switzerland Forum, with additional answer there.
The cheapest way? Hitchhiking!
Only the air is cheap in Switzerland. For student-level travel you should probably defer to Lonely Planet and Rough Guide.