Hi,
You may want to rethink using a joystick. Windows has changed the way it handles Joysticks. They used to be devices that plugged in to Gameports. Now they are USB devices that are considered as HID (Human Interface Device). Mach handles HID different than a joystick. This may cause you some problems.
The way that you get a device to work in Mach is to download the desired plugin from the Mach (Downloads - Plugins) and run it. It will place a DLL file in the Mach\Plugins folder. You then connect the device and start Mach. Then go to Config Plugins from the Mach main menu. If you see a red X next to the joystick plugin, click it to turn it green. Then pick Config and setup the joystick how you want it.
If you do not get the joystick to work properly, you might look at either the Shuttlepro plugin ($30-40 on EBay) or my XBox360 controller plugin (about $40 at most stores $20+ on EBay).
Good Luck