It's pretty easy to build a working pinhole camera; a search using Google for "pinhole camera" yielded 697,000 hits, not all of which (I'm sure) are relevant. Here are two that are:
Instructions for making the Dirkon paper camera (that uses 35mm film), originally published in a Czech magazine for young kids, can be found at http://www.pinhole.cz/en/pinholecameras/dirkon_01.html. The instruction can also be found in the .pdf document Dirkon Instructions. I've never tried this - if you do, please let me know how it worked and send a couple of pictures if you can.