You can get access to the public SVN repository at SourceForge.net.
If you are not familiar with SVN and how it works, please read its brief overview at SourceForge.net: http://sourceforge.net/apps/trac/sourceforge/wiki/Subversion.
Then, if you have a SVN client installed, use the following command to get the Anti-Grain Geometry sources:
svn checkout svn://svn.code.sf.net/p/agg/svn/ agg-svn
You can also browse the repository directly: http://sourceforge.net/p/agg/svn/
SVN