Trust me, just start with a basic CS-like set-up, and then tweak it to your liking. If you have a mouse with a wheel in the middle, it's awesome for this game. I use wheel up for zoom, wheel down for change weapons, and mouse 3 (press the wheel button down) for a melee attack.
Or, how bout this, you can use an xbox controller. I've heard before that it is possible, and fairly simple to wire an old xbox controller (take the controller s that I never use for example) to be inserted into a USB port like a standard computer joypad.
Found an article on this
here.
You can always just google "xbox controller" and USB and mod, and you can find another article if you wanna.