Thanks guys -- good sites! Put them all in Favorites.
To answer Photo Engineer's question -- 'why not just make a regular emulsion?'
I guess for the same reason I don't just use Liquid Light, or a digital camera and PhotoShop. I've always loved both the look of the old ambrotypes and the fact that those guys made them (literally) themselves. I most likely will end up going to gelatin just for the added flexibility, but I want to use albumen right now just so I can tell people 'I made it with egg whites'.

:-)