How can I install the Emerald package on Mint? I cannot seem to find and install it in the Synaptic Package Manager. I think the repository of this package is missing. But I don't know where it is and how to add it to the current list of repositories.
The emerald window decorator isn't available in the Ubuntu official repositories(Mint included) anymore, unfortunately, but there are other way to acquire it.
I am not aware of any PPAs for Precise, but building it from source is really straightforward. Here's a basic guide for 12.04: