This is how I made a waterproof case for my digital camera. It's not a super detailed instructable...more like a build-a-long. It's full of great ideas on how you can make your own...
One great hurdle this case solves is the camera interface. Mose DIY waterproof (hard) cases don't have a way of operating the camera's shutter. It's usually just turning on the camera and sticking it inside a box while it films.
My lake is frozen, so I'll need to wait until it thaws to get some good pics. I'm stuck with the sink for now!
This box is just an airtight food storage box from Dollar General (cost $2.00). If you don't have a dollar store nearby, Meijers ALWAYS has them in stock, but prepare to pay $3.00 and up. Just look in the Tupperware section :D