That is a WMS (web mapping service) server which provides "tiles" like those used by NJPB Live Maps. I don't believe there is a standalone viewer available. I can access it with Globalmapper and Ben can link it to the site however.
Nice job! The historicals are great and load very quickly for me.
NJPB Live Maps version 4.0 Released
Tested with Safari 4 and IE8.