Coincidentally, I was wondering something similar last night and happened upon this thread:
Underwater Camera? - U.S. Masters Swimming Discussion Forums
It's from 2003-06, but it gives some good information about issues to consider--particularly the posts by letsrace (Mike Ross).
I just purchased a GoPRO video camera system for my track bike (motorcycle). When it came I didn't realize that in the clear plastic, sealed case its waterproof up to 100'. I'll have to give it a shot in the pool!
http://www.goprocamera.com/