Thank you for this handy script.

There's a little bug though that doesn't allow you to switch weapons via mouse wheel after the game start. You should press either [1], [2] or [3] key for mouse wheel to start working as supposed (until the full game restart). To fix this just add

@slot1

as the last line of the script.

#12: And you forgot

bind MWHEELUP "prevslot"
bind MWHEELDOWN "nextslot"

when answering Aoshima's question.