Doug,
The properties you mention (XScale.Minumum and .Maximum) can be set while a vi is running. Make sure the property nodes are within the a loop that is currently running when you make the change. Also, make sure the control or variable you use to set these values is being read in the same loop. You'll also need to make sure the xscale of the graph is NOT set to autoscale.
I'd say since your seeing the property node "XScale.OldRange", the example you're using was probably from an older version of LV. When property nodes change, as Xscale did, they support the old versions. Use XScale.Range in your new applications.
Tim