Then you have a selection of packages:
http://www.hypeskeptic.com/Mattias/DelphiODE/
http://www.newtondynamics.com/downloads.html - Sascha Willems maintains the headers for Delphi.
http://www.partow.net/projects/fastgeo/index.html


Of course i can read many clever books and many codes and do more. But if you ALREADY know how to improve it, why not to improve it? Is it so hard? To write some formulas.
Assuming someone has the time to put the effort into it, then no it isn't hard. Physics engines are powerful tools and to create or find an opensource one is almost as hard as making it yourself! That's why they sell them, because they make it as optimized as possible and as flexible as possible for your games.

I don't really know much about physics, but all the work I have done with vectors, color transformations, and even a small game have been opensource under the MPL. But I can learn, and it doesn't intimidate me.