Some time ago I upgraded the subversion server to subversion 1.5, and the clients that use it are probably mostly on 1.5 as well. We haven't had any compatibility problems between versions on this upgrade, which is good news since a few versions ago there was a release which caused any newer client to render the repo unreadable by any older client. Predictably someone in the office upgraded their client one day and it took us a good few hours to work out why subversion had stopped working!
The Subversion 1.5 upgrade doesn't turn on all the 1.5 features by default, but will upgrade to 1.5 and allow older clients to continue to work with it. If you want to upgrade to the 1.5 features though, you'll need to make sure that all users have clients of version 1.5 or later, and then upgrade the repo by running:
Once this is done you can start using the new merge tracking features in subversion - enjoy!