From my understanding I believe that you would want to create at least one branch (maybe two if you want a development and a release branch)
So svn cp -r5 file:///path.to.repo/trunk file:///path.to.repo/branches/development
would be a typical way of creating a branch from an old version of you code.
This basically copies how the trunk directory looked at revision 5 and puts that into a new location "branches/development"
Now I'm assuming that you setup your repository in the standard svn way (with trunk, branches and tags), regardless of this setup it is still possible to use this command.
You may also be interested in the svn switch
command which allows you to switch your working copy from one area of the repository to another. Alternatively you could just checkout 2 workings copies (depends on how much disk space you require I guess)
Take a look at svn redbook for more information on commands etc. in svn: http://svnbook.red-bean.com/