I did a checkout from my trunk to a local DIR and made lots of local changes there. Now I don\'t want to commit it back to the trunk, but I\'d rather make a branch from this loc
Yes, you can do this by SVN commandline as well as tortoiseSVN.
You have to specify your SVN workingcopy as src and your new branch as destination of the
svn copy
command.
In TortoiseSVN just point into your working copy, choose "Branch/tag" from contextmenu and choose "Working copy" in the section "Create copy in the repository from:"
Note that it is not a good idea (for traceability reasons )to create tags in such a way, but for branches it is perfectly fine.