If someone who is more knowledgeable than me about this could write a brief synopsis please? It would be great if this had an emphasis on the originals which have resulted in the various garden models. Otherwise for the moment I refer readers to the Wikipedia in the links section below (JSJ).
The Wikipedia page on Baldwin Locomotive Works seems comprehensive is at http://en.wikipedia.org/wiki/Baldwin_Locomotive_Works#Steam_locomotives
There is a downloadable version of the Illustrated Catalogue of Locomotives (1871?) at http://www.archive.org/details/baldwinlocomotiv00baldrich
A web page with lots of narrow gauge Baldwin information which includes the design details for the Biles-Coleman mallet that was modelled by Bachmann
A web page giving a run down on how a locomotive was built by the Baldwin locomotive Works (BLW). A must read,