I was asked where to get the old serials - fortunately, a lot are available on DVD.
Then there are LEGAL Torrents & Rapidshare (as a lot are public domain now) or places like this -
The Adventures of Captain Marvel (1941)
The Phantom (1943)
Captain America (1944)
UNFORTUNATELY - Batman & Robin (1949) is NOT public doman, but can be bought quite cheaply if you look around.
Amazon US - Batman & Robin (1949)
Amazon UK - Batman & Robin (1949)
Next - onto the 50's - the glory of TV!