Also look at using Keygrabber to map the buttons and joysticks on the gamepad to whatever function you want.
Once Keygrabber is up and running to suite your tastes, you can modify the Mach3 shortcut to start Keygrabber "automagically".
I believe Keygrabber is included with Mach3 and should be in the C:/Mach3 folder if you installed Mach3 to the C drive.
I currently use one of the Logitech game pads and it works great. While for my mill I would like to have some more buttons, it has been working very well for me.
A nice feature of Keygrabber is that you can set one button to change pages and then you can have 4 pages of buttons on the same gamepad. On each page the same button can have the same or different functions.
Let me know if you need more help.
Mike
Warning: DIY CNC may cause extreme hair loss due to you pulling your hair out.