Trac is a wiki and an issue tracker put into a blender and set to 10. Needless to say, it is a great tool for every software project. trac talks FastCGI if we run trac that way. Getting the newest trac version from Subversion seems pretty much a good idea, as the old versions have a lot of dependencies that the trac team removed, but they apparently never got around to releasing a "stable" version since then. The bad news is that we will need a local install of Subversion (look at http://subversion.tigris.org). But we can remove it after we have retrieved trac from the repository, or use it integrated with trac.
Setting up trac is a tedious task, even without Lighttpd. So in order to rule out errors we should first set trac up as a standalone server and see if it runs. We can bind it to Lighttpd afterwards.