svn copy -r 68 http://subversion/svn/ projectX/trunk/ http://subversion/svn/projectX/branches/branchname -m "wonderful version"
Creates a branche of trunk (in revison 68) with the name wunderful version. Found in Version Control with Subversion. One has to go to command line because TortoiseSVN and Subclipse don´t support this method.