Hey John,
I got to play around with the G100 yesterday.

Only because my phase convertor for the spindle had to vent some smoke.

I have the analog inputs and outputs working here now. You are right, Analog input 4 is the top one in the monitor, 1 is 2nd, 2 is 3rd and 3 is 4th. Also in config. screen for the G100, spindle control, the analog output 1 is pin 4, 2 is pin 1, 3 is pin 2, and 4 is pin 3. Hopefully, all of this will change. The 4 inputs you see in the config, ports and pins, input signals has nothing to do with these as far as I can tell. Also, if you need to know for a macro pump, analog input pin 4 is input 124, 1 is input 125, 2 is input 126, and 3 is input 127. You should be able to, on the spindle setup tab in ports&pins, enable modbus spindle speed, at register 64, wire your spindle control (VFD or similar) to analog output 4 and cotrol it with Mach. Go to the MDI page, give it a m3 s ?*********, raise and lower the speed with the controls on scren while watching the G100 monitor. You won't see the monitor vary if you don't have the spindle runnig. You can also use an analog input to control an analog output, but you will need to do some work with VB. You need to have a macro pump or if you allready have one, you will need to add the code to do this.
I can control my feedrate with an analog input but there is a problem. I have code in the macropump (Thanks to Poppabear and Art) that will allow me to turn a pot and the feed rate slider goes up and down as it should. The problem is, the actual speed of the machine does not change. This is being looked at by the Grandpoobah allready.
Hope this helps,
Brett