D1+D2: Manage source code compatible components?

Hi,

I have a couple of components which are source code compatible, with
the odd {$IFDEF VER90} included in a few places.

Now I am looking for an intelligent way on how to maximize
code-sharing between Delphi 1 and Delphi 2 and minimize errors by
maintaining a SINGLE code base:

How can I make sure that all my components for both Delphi 1 and
Delphi 2 are compiled from the same source + (and this is the
difficult part) how to manage the .DCR and .RES files (why could
Borland not use a different extension for each version!?)  ?

Any ideas greatly appreciated!
TIA Stefan
--
Stefan Hoffmeister                       Stefan.Hoffmeis...@Uni-Passau.de
University of Passau, Bavaria, Germany