Minecraft and Multiple versions of Forge and mods

Minecraft enables you to play multiple versions of the program and multiple versions of mods.

Installing Forge

Forge is a useful utility which enables the easy addition of mods. You no longer need to copy Java class files into the .minecraft folder and delete the META-INF folder. Instead you install Forge and then copy files to a mods folder.

You can download Forge from here.

The following instructions are courtesy of mod-buildcraft.com:

Go to http://files.minecraftforge.net/ and download the installer recommended for Minecraft 1.6.4. The download link is going to bring you to an adfly link that might look weird at first. This is a sponsored link used to remunerate the developers of the Forge for the work they're doing. You should see a page like this (probably with a different advertisement in the body):

Note that on the top right corner, the count-down for the download. Just wait the 5 seconds, until the top looks like:

Then click on the “Skip Ad” link. This should download a file with the .jar extension. Click on it. You should get the following installer:

Click on OK on the bottom left corner, up until the success message. Then open the Minecraft lobby again, and switch profile to the Forge profile:

Hit play. The Minecraft lobby will then offer to log on the Forge profile with the same user as the one currently registered. Hit Play again to validate it:

And then back to the lobby, hit Play one last time. You should now see a Minecraft menu with Forge details displayed:

That's it! You successfully installed Minecraft Forge. Close Minecraft for now.

Multiple verions of Forge and Mods

When using Forge and the Minecraft launcher, by default all mods are stored in

%appdata%\.minecraft\mods

This is the global mod folder. However it will cause problems if you put a 1.6.4 and a 1.7.2 mod in here.
To get around this, use the GameDir setting in Minecraft.

Create a folder, such as %appdata%\.minecraft\mods\GameDir\Forge 1.6.4. Set the folder to this.
Run Minecraft again and it will create a set of subfolders within this, including the mods folder.
Put your version-specific mods in here.