Jerome, if it's just that you can't figure out how to use the ns_db
API, you need to read and practice more. Perhaps look at the old
OpenACS 3.x code for lots of ns_db examples.
However, it's not that hard to to a pretty cleanly modify the OpenACS
db_* ABI to let you use it on multiple database, and database you have
an AOLserver database driver loaded and configured for. I did it for
ACS 4.2 - see
this thread.
I will volunteer to do a further cleaned up and better tested version
of that for OpenACS when I have time, probably for 4.7, or perhaps a
later maintenance release of 4.6.x (as the changes can be made
entirely backwards compatible).
But if you really need something like that now, take a look
at my old 4.2 code, and let me know if you have questions.