Minecraft Version Changer changes the version of your copy of Minecraft automatically.
Minecraft is a sandbox-like game. There are two versions: the Beta version (that will be launched on November, 2011) and the Classic version, that you can play for free when you are logged on a server. In the Classic version the players can build fortresses by using cubes, but they will not have all the challenges that the Beta version offers.
Minecraft Version Changer updates the installed version automatically. This way, you can play Minecraft instantly. If your installed version differs from the one that your server is running, you will get a "server outdated" message, and you will get disconnected. This program allows you to avoid that. You will be able to choose the version number that you want to use from the included list of versions. The program will check if there is any new version of the game available, before you try to connect to Minecraft servers.
This program enables you to choose earlier versions of the game, too. That makes sense if you are connecting to a server that didn´t change the game´s installed version. By changing your version, you will be able to play flawlessly.