The registration is a bit broken at the moment, but it's not necessary to be registered to view the source and/or contribute.

If you register to the mailing lists listed at http://www.limewire.org/project/www/MailingList.html (especially the core/gui dev) you can see discussion is active.

You can also view the code for the core, gui and tests by choosing the appropriate module at http://limewire.limewire.org/servlets/ProjectHome and then choosing "source" at the top. From here, you can either view the code in your browser or follow the instructions to download it via CVS.