JC,
I don't know for sure if this will answer your question, but you might want to look at:
http://docs.moodle.org/en/Authentication
http://docs.moodle.org/en/External_database_authentication
http://moodle.org/mod/forum/discuss.php?d=75519
RLE
Installing and upgrading help
use remote database for login but password internal
This discussion has been locked so you can no longer reply to it.