Ask HN: Internal Networking at a Lean Startup

First time I've tried an 'Ask HN', so I'd appreciate any feedback on how I might clean this up:

I've tried searching the web, serverfault, etc. for what I'm looking for, and I always either end up empty-handed or come away with recommendations that are far too complex (I hope) for what I'm looking for.

Our company was once much bigger and with a different focus (primary ASP.NET/C# web development) and could support 1-2 Windows Networking "Guys". Now, we're much smaller, our focus has completely changed, and we rely primarily on open-source (particularly Ruby/Rails on Ubuntu Server).

Unfortunately, I'm splitting my time between new-app development and maintaining the aging internal Windows domain (where I have little to no expertise). At this point, the only benefits we get from the Windows domain are 1) internal dns, 2) an internal file-server, 3) vpn access into the office, and 4) whatever else comes with active directory (we've since migrated email onto a hosted service).

I've been given the go ahead to pare down setup down to the bare minimum as long as I can meet the following requirements:

1. Need to be able to access servers internally (i.e. add a nightly build on a local machine and access it via http://nightly or whatever) 2. Need to have a file server with certain "protected" directories 3. Need to be able to VPN in and access said servers from the outside world

How do small (< 15 people) companies usually handle this? I'm looking (hoping!) for a guide that starts at "So you have a static IP and an internet connection into your office" and then walks through setting up an internal network from there. Most books I've found assume I want to know everything about the network stack.

Any suggestions on where I might look for answers?