This page:

http://www.sncf.co.uk/default.asp

has tabs across the top that describe each service of SCNF.

In addition, the Metro and RER cover Paris and the surrounding region in much the same way that NYC and other big cities have the subway and commuter trains. Think of the Metro and the subway and the RER as the commuter rail network. The twist is that the tickets are interchangable within the main portion of Paris itself, with a Metro ticket letting you use the RER within the core of the city. For example, by far the quickest way to get from Notre Dame to the Tour Eiffel is to take the RER C instead of the Metro, using a regular Metro ticket. A twist that I don't recall seeing in most other places.

If you're interested in Alsace and want hotel/restaurant recommendations, PM me and I'll dig through my old files.

Your mention of hiking reminded me to mention the Paris Walks people (described in other threads). The people are great, and we especially enjoyed the Montmartre. http://www.paris-walks.com/ Most of the tours start/end in a very central spot, making it easy to combine with something else on your agenda.