I found ZedGraph, which is a sourceforge project for "creating 2D line and bar graphs" - exactly what I wanted. I spent some time writing code to parse the file into time events, and adding new commands to the server to retrieve the data.
I knocked out a quick GUI, which is not fully functional yet, but it demonstrates what I want to see.
Below is a screenshot of a graph for December so far...
For some reason the graph always leaves the first label off the x axis, but thats really only minor in the grand scheme of things!