[crocos]

Now to install your mod:
Close Minecraft (don't need to close the launcher)
Open Windows Explorer and go to %appdata%\Roaming\.minecraft\
Create a folder called "Mods" under that, then create another folder called "1.6.4" inside the Mods folder.
Put your mod inside the 1.6.4 folder you just created (even if the install instructions for the mod say "put in mods folder", put it in the 1.6.4 folder unless it explicitly says to "not put in the 1.6.4 folder".

You should now be good to go - launch Minecraft on your Forge profile (which you may wish to rename "Forge 1.6.4" at some stage)

You can now also delete the temporary clean "new profile" for 1.6.4 - that was only to ensure you had a clean copy.