Here's a small script to add a new folder [NEW_DIR] to your svn repository at [SVN_REPO_URL]:
svn co --non-recursive [SVN_REPO_URL]/trunk trunk
cd trunk/
svn mkdir [NEW_DIR]
svn ci -m "added [NEW_DIR]"
cd ..
rm -rf trunk/
svn co --non-recursive [SVN_REPO_URL]/trunk/[NEW_DIR] [NEW_DIR]