There is a wiki for collaboration here.
You may also view these videos about Plone and software development:
At this moment, the repository is not open for public access, which might well be a mistake ;-) However, you may be granted access if asking for it through our contact form: http://www.openmusiccontest.org / contact-info
A good idea is to have your public ssh key ready to send to us, so we can put it on this server for password-less authentication and repository access.