This is cool. Here's a step-by-step guide which shows you how to give your DSLR a 250ish f-stop pin-hole lens!
http://www.camerahacker.com/EOS_Pin-Hole_Lens/index.shtml
Also look at the bottom of the above linked page for more interesting projects.
Some more DSLR hacks found on Wired - my source for the DSLR pin-hole project:
http://blog.wired.com/gadgets/2008/04/four-camera-hac.html
Have fun.
Best,
Kurt