OpenGuides source is now held in a subversion repository at https://urchin.earth.li/svn/openguides/. The repository can be browsed with a normal web browser, but to work properly with the code you will need a Subversion client. The rest of this document assumes you have found and installed a suitable subversion client.
You can also browse the repository in a more detailed fashion by using the "Browse Source" function of Trac.
The repository is SSL protected (primarily to protect authentication passwords) but the certificate is not signed by a well-known CA. You can find out more about the CA and get the root cert from http://www.earth.li/ca/. We recommend that you install this in your browser and subversion client. To install it into your client, download (and preferably verify...) the earth.li-CA.crt file from the site above, put it somewhere convenient and point at it in your ~/.subversion/servers file (if that directory doesn't exist, run "svn help" to create it):
ssl-authority-files = /path/to/earth.li-CA.crt
Checking code out from the repository is allowed by anyone, but to commit, you need to persuade Dom <dom@…> (the current maintainer) that you should be given access, and supply him with a (preferably GPG signed and encrypted, or placed on a shell machine that he has access to) line for an Apache .htaccess file. You can do this with the htpasswd tool:
htpasswd -n your-chosen-username
See CommitPolicy for more on committing code to the project
For now this is a very basic guide. If you've used CVS this will be familiar...
svn co https://urchin.earth.li/svn/openguides/trunk openguides-trunk
You should only work in the trunk/ subdirectory unless you really know what you are doing.
There is a mailing list at http://urchin.earth.li/mailman/listinfo/openguides-commits which you can subscribe to in order to receive a log message and diff of every change made to the repository.
There is a very good book about Subversion available online and in print from http://svnbook.red-bean.com/.