Here a stolen answer to another question (thanks Maciej Łebkowski!):
From my experience: don`t put that file under version control and use svn:ignore on it.
It’s a little hard at the beginning, since you cannot ignore a file that is allready under version control, and you cannot remove a file from version control without removing it from hard drive (and from every working copy on next update...). But when you finally manage to set up the repo correctly, it works like charm. Don’t forget to add a generic-template in place of your original config file (so that everyone knows about new config variables, and so on).
For new repo:
mkdir config
svn add config
svn propset svn:ignore '*.conf' config
For existing repo: be sure, to have a backup of your config in every working copy, then remove (svn del) config from the repo, commit (please note: the file will be deleted in every working copy on next update! you have to have a backup) and then restore the file and set the ignore property.
Another way is a lock. It guarantees that noone commits the file, but it will result in an error on every commit. not very nice.
And the third way - changesets, a new feature in SVN 1.5 clients. This is neat, but it’s only related to one working copy, not to a repository globally. And you have to set them up manually, add every new file — it’s hard to maintain.