For each release, the source code can be found on the Download page.
VitaminSEE development is done in a public SVN repository. Adium’s GettingAdiumSource contains a good overview of SVN and how to install and set up SVN on your local computer.
The repository is meant mainly for developers and for people who want to contribute to VitaminSEE’s development. The trunk of VitaminSEE is not guaranteed to work, and sometimes doesn’t even compile.
The repository is located at http://svn.elliotglaysher.org/VitaminSEE. If svn is installed on your computer, you can check out a copy of the code with the command:
svn co http://svn.elliotglaysher.org/VitaminSEE/trunk VitaminSEE