Under the PSF bylaws, in order to become a voting member you must be nominated by an existing member.
The bylaws do not, however, require that directors be members. Board elections are coming up soon, and so anyone interested in becoming a director is invited to nominate themselves, by editing this Wiki page. There is a link on that page to an outline of the duties and responsibilities of being a PSF director.
As chairman (at least until after the elections) I would be happy to see more competition for the places on the Board - I think a change of lineup from time to time is a very healthy thing, and makes it more likely that new ideas and approaches will emerge. A board seat should be more than just a line to add to your resume - it is also an opportunity to serve the Python community and take a broader role in the open source world.
Nominations close on Friday February 5, so think about nominating yourself, or (with their permission) somebody else you think would be active in managing the Foundation. If you want to discuss the possibility before moving ahead with a nomination please feel free to email me as chairman at python dot org for more information.