I'm wanting to become conversant in the use of the Standard Template Library. If I come across a general reference or beginner's guide published around 1995-97, can I rely on the information in it? How much has STL changed in the last dozen years?
Not a whole lot, if at all. The current standard was published in 1998.
cplusplus.com has a more up-to-date reference, which you can compare for yourself.
I'd recommend also that you get a copy of Scott Meyers' Effective STL.
Yes! There are new additions. The TR1 update is now implemented in most environments.
Your older book is still useful to learn the basics. But you will want to find a reference for TR1 to learn about some very useful new features. In a couple of areas, the new features are preferred over older ones. (What comes to mind is bind1st and bind2nd functionality is fully encapsulated in the more general bind construct.)
In addition, there are the boost libraries. (boost.org) Boost is a a collection of libraries, some are very useful, others are obscure. Some of the features in TR1 came from boost, so there is some overlap. There is at least one good book about Boost out there.
I like the SGI reference to the STL
http://www.sgi.com/tech/stl
Which includes a set of resource for further reading
http://www.sgi.com/tech/stl/other%5Fresources.html
I think that this documentation was done by the crater of the STL (could bee wrong on that).
But the STL has not changed since it was made official. The new additions for TR1 are currently not officially available but will be part of the new standard. Though you can grab them via boost. Which is another set of libraries you should look at.