The scenario: I had an OS X Server which I had been accessing via ARD (Apple Remote Desktop). I had recently updated the ARD Client software to v3.1. This morning I needed to install the ARD Admin software on the same server (to use it as a Task server, probably the most useful feature of ARD 3). No joy. The installer complained that the software already installed was a later version than I was trying to install -- 3.1 Client on the server, 3.0 Admin on the install disk.
The reason this happens is that the ARD Admin installer package is actually a metapackage -- a package of packages, if you will. It contains a package for the Admin application and also one for its own version (3.0) of the client software. It's this package that's blocking the install.
The solution is a simple, if not immediately obvious, one. Control-click on the RemoteDesktop.mpkg icon and choose Show Package Contents from the pop-up menu. In the new window that opens, burrow down through Contents -> Installers, and find the RemoteDesktopAdmin.pkg installer. Double-click on that one and ... Presto! one fresh clean installation of ARD Admin.
But it doesn't stop there, sorry. The last thing you must do before launching it is update it with the ARD Admin 3.1 updater. You can use Software Update or download it from Apple's update site.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061221074336970