Ultimately software will assist doing this.  Microsoft Visio has many features which make is possible to draw networks.  GoVisual 1.0 is a plugin to Microsoft Visio which automates diagram layout. There is great article on Go Visual @ EWeek "GoVisual Cleans Up Visio Designs".

A good start is to just to start.  Sit down with Visio and put in a couple of your nodes, details are important, it is better to start with too much then having to keep adding it later.  If you have a database of network information, this can help, link this to Visio and use it to make the diagrams complete.

Define some type of hierarchy which will allow your network to flow across several pages.  It is important to avoid clutter, it is better add details in a drill in.

Taking the resulting diagrams and convert them to HTML and publish on a web server which is secure and available to people involved in the operation of the network.