There is a glue adhesive remover that's very nasty to work with. We have a friend in the flooring business and he uses it, but I have to warn you, it's terrible stuff. Might try going to a local flooring guy and see what he suggests.

Rudy-
With flooring that old, there is a high probability that it (and/or) the adhesive contains asbestos. Before you disturb this any further, you should take a small sample to a test lab to determine whether it's present. Here is some general info:

Asbestos in flooring