You can use your favourite SVN client and connect to our SVN server at http://svn.xvid.org.
Here's some example commandline that shows how to checkout the trunk sources (when asked for password, leave it blank and hit enter):
svn checkout http://svn.xvid.org/trunk --username anonymous
This is Xvid 1.3.7 bugfix release. It fixes and replaces the previous 1.3.6 stable release.
You can read a more detailed description of the changes in the ChangeLog file available in the top directory of the inflated sources tarball.