This instructable will show you how to build a pistol-grip mouse for first person shooter games.
(note: these instructions were made after the actual device, so the pictures are of the finished product disassembled)

Step 1: Preparation...

You will need:
1 old joystick (just the handle/trigger thing)
an old optical mouse
soldering iron (you can build it without soldering, but it's not as reliable)
hot glue, duct tape, third hand, molten plastic or whatever to hold it together.

Step 2: Take Them Apart!

Open the joystick handle and identify the wires for each button.
in this case, the trigger wire is red,
the top button is white,
and common is blue.
(common is a wire that connects both, so you only need 3 wires instead of 4)

Step 3: Mod the Mouse

solder or otherwise attach the wires from the joystick to the mouse buttons.
i chose to use the trigger (red wire) for the left button, and the top button (white wire) for right.
find the common terminal by following the circuit traces, there will (should) be one wire/trace going to both (in this case 3) mouse buttons, this is where you will attach the common wire.
On my, and most other mice, the common is the ground. (the negative power source everything connects to)

Step 4: Physically Attatch the Mouse to the Joystick.

this is the most difficult part of the build, and unless you have the exact same mouse and exact same broken joystick, you'll need to be creative and figure this out yourself.
but, If you do happen to have the exact same mouse and joystick you can hammer a pen onto the screw anchor thing, and use the joystick's screws like a vice to clamp the joystick to the pen.

Step 5: Results

After years of using a normal mouse, i've developed a nasty calice on my palm, and after an hour of playing games, my fingers ache like crazy! using the joystick mouse is much more comfortable, and i'm able to aim and shoot faster. It's a little awkward for regular computing tasks, but that's just my opinion. your mileage may vary.

Step 6: Going Further...

I've just added a scrollwheel as a replacement for the top button (the button was old and not working right anyway) it also serves as the right button, i may add the middle button, but not soon, it was hard enough to add the wheel. I will post pictures soon. (but i will NOT show the inside as i probably won't be able to put it back together again without problems, but i will provide ample explaination)