Is it possible to download and mess around with old puzzles that have been closed? I'm fairly new to foldit and I wanted to take a look at a few other puzzles to get my feet wet.
I think you have to open a puzzle before it expires to be able to play with it after it expires. Another idea is to play one of the Contests.
http://foldit.wikia.com/wiki/Puzzle_Results shows images of various solutions to old puzzles. Some, like puzzle 62 (see http://fold.it/portal/node/293128), have videos showing how the shape of the protein changed as the score rose.
Sadly, you can't. Would be a nice feature though... I have thought that turning an expired puzzle into an available gallery would be nice.
(As Jeff said above)^^