Don't you hate it when you remember seeing a webpage but can't remember exactly how to get there? This one took me a bunch of judicious web searching to finally uncover again. It basically details how you might go about making an SSTV demodulator, some of the details of which I was a bit sketchy on. This page not only gives you the answer, but shows some of the mathematics that makes you have some confidence that what you are doing is right. I'm too tired to figure it out tonight, but I'm archiving it for later:
The ISS should be operating SSTV on August 3 and 4, using the Robot36 mode. I'll go ahead and see if I can catch some pictures from space that way. Should work well, after my success with AO-51.
Addendum: If you want to test your SSTV software before hand, you might want to use a recording that I made. Go here and fetch the linked .wav recording, and use it to test your SSTV software. It will also help you know what an SSTV signal sounds like.