Using GIT to merge folders?

I have a Magento installation that is using G开发者_开发技巧IT to maintain the code revisions for our theme design changes etc.

Once in a while we use third party plugins that are provided in a zip file. As an example, the file structure would be something similar to the following:

/app
 - /code
 - /design
/skin
 - /frontend
 - /m

The directories only include files that need adding to the Magento installation,however if I simply drag and drop on my Mac - it replaces the directories, losing any files that aren't included in the new plugin files.

Is there a better/easier way to pull a plugin into the installation using GIT?

You could just place the zip file in the Magento root directory and run unzip from the command line, that doesn't do the silly "obliterate the current folder contents" that the GUI does.