Question: I want to set up a source code control system that:

1. is networked, so users can access it at work or on the road
2. does not need to provide sharing, lock mode is sufficient
3. there will be only three users and they will never be working with the same code
4. we have no system administrator and not much knowledge in that area so the set up and config must be dead simple.
5. will be installed on a Windows server
6. open source or free

Suggestions please.

Answer: 
The simplest version control system I am aware of is a **Revision Control System RCS**. It is a command line utility that is available out of the box on Linux systems. It's usage is quite simple.

**First.** Inside current directory, create a directory where RCS's information will be stored:

```
$ mkdir RCS

```

**Second.** Store (check-in) a file into RCS:

```
$ ci -t-"My notes" notes.txt

```

Original file gets deleted. 

**Third.** Restore (check-out) original file from RCS:

```
$ co -u notes.txt

```

**Fourth.** Edit file as needed, now it can be restored any time:

```
$ vim notes.txt

```

RCS is also working with binary files, and supports many subsequent changes to a file.
Lots of recommendations for SVN, but I'm not sure I'd call that "simplest" from an admin point of view. You still need to set up a server, IIRC. In comparison, a DVCS like Mercurial makes no distinction between "repository" and "working copy". To put something on a server (which can be any folder you have file-sharing access to), you can just "push" it there.

You also mention working on the road. DVCS are particularly good at this. Your laptop will have the whole history, so you only need to touch the server if you want to push or pull, not just to do a diff or check the history.