Creating Joypad/gamepad, how? Please read.

Hi, first post on the forums.

I'm a games programmer and run my own small-time company. I know a little about hardware, but not enough.

Basically, I am trying to create this joypad for use with my games. I, of course, would rather mod an existing controller.

The closest model to my design is the 'Invader Gamepad'.
Please view this picture (paddesign.jpg, jpg file) (URL address blocked: See forum rules)

4-way d-pad
4 main buttons
Extra button
start/other button
2 shoulder buttons.

The invader pad has:
8 way directional d-pad
4 main buttons
Analog Control Stick
4 Shoulder Buttons
Start Button
Select Button

I will be taking the casing away and making a new one, with holes only for what I want to be there.
The 'select' button will not be included on the pad, but the round button near the d-pad will use this place instead.
Will I need to make some sort of lever system or something to push down the button place on the 'CPU' board inside?

Thanks for any help, and sorry if this is posted in the wrong section.

Joe