To set up a project, you can use several methods. There are several popular Subversion clients, including Eclipse (with Subclipse), Tortoise SVN, Rapid SVN, and the good ol' command line.

Change to the directory you want to work on your Vufind instance and then run this command

svn co https://vufind.svn.sourceforge.net/svnroot/vufind/trunk vufind

This will check out the Vufind source into a folder named vufind.

As a side note, don't forget to export the code if you are planning a deployment:
svn ex https://vufind.svn.sourceforge.net/svnroot/vufind/trunk vufind
This removes the .svn files and will greatly reduce the file size of the package