First time I'm trying to do a deploy from Visual Studio (2012) using the Publish option to my test server.

After some initial issues where I found the answer in this discussion I can now see my site correctly.

When I want to add a module, I get the following error 

Package installation failed: Unable to backup existing local package directory.

Any ideas?

Ask the WebDeploy folks, that looks like an error on their end. I would guess insufficient permissions.