(This is still a work in progress, please ignore typo's and weird gramatical bits for the moment)
JFFNMS is a php front end to rrdtool graphs. By default it will walk through an snmp device and auto-detect any standard SNMP interfaces it can find, such as CPU information, byte counters per network interface, etc etc.
If you want to make JFFNMS graph other things, such as SNMP information out of a custom MIB, you need to add support into JFFNMS to do this. Once the support is into JFFNMS, it will allow you to monitor that interface on all machines, and if you have Autodiscovery enabled for a host, it may even automatically add the graph with no user intervention.
Unfortunatly the user interface for JFFNMS could do with some work, and the documentation is not much better.
For my application I wanted to monitor a new SNMP based temperature and humidity sensor (http://dcf.sk/microweb/snmpmain.html) we purchased.
This assumes that you have got JFFNMS installed and working correctly, and that you have some understanding of how to write PHP and how SNMP works. This is based off of version 0.7.5 of JFFNMS. Earlier versions have a different UI and way to edit the fields.
Some JFFNMS terms:
There are actually inter dependencies when creating these things, so you have to create them in a specific order, and often have to go back and add bits once you have created more stuff.
You also will probably have to write some scripts, such as an auto discovery script and perhaps a custom poller and/or a custom grapher. More about those later.
This section details the configuration you need to do using the web frontend to add a new custom Interface type.
Goto Administration -> Internal Configuration -> Polling and Discovery -> Interface Types
The fields are as follows: