What should I use?

OK, I am currently in the planning stages of a web site I am putting together and was looking for some suggestions as to what I should use for the features I need.
A registration system for a large (>1000) number of people. (database? but which one?)
A small number of non-technical users (approx. 15) need to have access to this database through a web interface.
I also need those same users to have access to a basic messageboard system.
A different group of users (approx. 20) need to have access to a seperate messageboard.

Any suggestions as to what might be the best option for me? I was looking at mySQL and PHPNuke but I am not really sure. Thanks in advance!