The X-Box gamepad doesn't have analog buttons, I'd be interested to know how and why yours would/does.
Also you can pick up the parts to create an X-Box -> PC Lead from Maplin for like £3 if that.
It isn't that hard to do.
As for gamepads as good quality with as many buttons.
I have the Gameware USB Rumble Controller, and the Gravis Aftershock USB Controller.
Both of them have 12 Buttons, 4-Way Direction Hat, 2 Analog Sticks and full Force Feedback through 2 Motors.. Right<->Left Controls the Left (stronger) motor, the Up<->Down Controls the Right (weaker) motor.
Drivers for both make them work with almost every game title, in-fact you can setup the Gravis Aftershock to emulate any number of combinations you choose. So games that don't even had Gamepad support can still benefit from it.
The Gameware one is £10, the Gravis one is £20.
That is ALOT cheaper than your solution.
This aside, your drivers (if they've been developed correctly) should be useable directly with DBP. As I've not seen any 3rd party PC drivers for the X-Box controller I don't know.
I found when I connected the controller Windows XP instantly recognised it as a 6 Button Joypad with 2 Joysticks and a POV Hat.
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