Your internal server needs to be running a web server and have mysql and apache configured with it also.
If it's ONLY going to be for internal use, and you're sure nobody is going to try and do anything malicious, then just (I'm guessing it's windows) install
EasyPHP to get it setup quick. It's designed really for php developers to work on things locally so it's not hardened security wise, but it works and will run SMF and the like fine.
You'll then need to edit some of the config files (it's easy, I can upload an already edited one) to make the server listen to other requests except from itself (easyphp is designed for testing / working with php on), and then it'll act just like a regular web server on the internet. Read up on the site for guides and stuff, it's not too hard =x.
I have an exact copy of the RMRK forums that I run on my own pc using easyphp, for testing anything I write before applying it to the real RMRK. It also acts as a backup and stuff.