Ok.

I seem to have resolved the problems I indicated.

The dbmopen issue was, it appears, the result of an untidy (to say the least) uninstall of Cygwin which left dozens of files scattered across my root folder, i.e., C:/. The DB_File question (this is embarrassing) could have been resolved much faster if I had simply asked google (please see below):

http://code.activestate.com/ppm/DB_File/

Since I am using a 32-bit Windows XP machine, the reason why I was unable to load the file and the repository I was using did not show it as being available was, alas, immediately obvious when I visited that link.

Thanks.