I wrote an automatic map installer for Portal 2.
All you need to do to install a map is to save a fresh map or map archive (zip, rar, ...) into
Documents\Portal 2 Map Downloads (can be changed at will)
and it will get installed instantly.
You can even start the new map from the Extras menu.
For the relevant links refer to the information in my signature.
Edit:
I totally forgot to mention that the program is capable of installing .vpk files - even though .vpk support is broken since the DLC. It does that by unpacking the .vpk (vpk files are just a fancy type of archive) and installing the individual files in it.
However, this requires the developer tools to be installed. The program provides a menu option to install these.
