Hey Lynn,
I just posted a reply to swisscate who asked the same question.
check out all the links i listed there. (Mods: how do i make a link?)
400-800 will get you a room in a share-house. the further you're prepared to travel the cheaper this will get.
If you are a student you should be able to contact your uni/institute. I know ETH has a service providing subsidised places and if you're a post-grad they can (maybe) find you a cheap apartment. I would definitely start with your uni/supervisor/group secretary first.
also try
http://www.woko.ch/ http://www.international.ethz.ch/coming_ch/housing.html
this site was really useful and i'm not even a student (anymore), check out the links on cost of living etc. so you have an idea what you'll be spending.
good luck
Nic