Here’s a nice article of how to install SharePoint 2013 on a Server, which has no internet access.
http://www.dontpapanic.com/blog/?p=241
The Problem here is, that the prerequisites package will always try to download the setups before installing them. There’s of course a workarround to download the packages manually and then trigger the prerequisites setup with the needed parameters.
Once completed, you will need to restart the system: