Download Rei's Minimap from:
Go to C:\Users\USERNAME\AppData\Roaming\.minecraft\versions
Create a New Folder called "1.6.4r"
Copy and paste .jar and .json from the original 1.6.4 folder
Open the .jar with winrar and put in Rei's Minimap files
Delete the META-INF folder in the .jar
Save the jar
rename the .jar to 1.6.4r.jar
rename the .json to 1.6.4r.json
open .json in text editor
change id to: "id": "1.6.4r"
Set version to play in profile of launcher
Enjoy MiniMap