If you acccidentally delete a .svn directory from a folder that is under version control, you'll get an error when you try to commit and won't be able to proceed. A real quick fix, that worked for me, is to just check out a new copy of the repository, and copy the .svn directory you deleted to your current working copy and you should be able to commit.
$ svn co svn://server/project project $ mv project/path/to/dir/.svn working_copy/path/to/dir $ chmod -R 777 working_copy/path/to/dir
You may not need the chmod 777, but I was getting a permission denied error before that. I don't know what negative effects this could have on your repository, so proceed at your own risk.