the scroll wheel button is button 4. so
if mouseclick()=4
will detect the scroll mouse button.
..
you're probably wondering why it's 4 and not 3.
well it's because button 1 is 1, 2 is 2, 3 is 4, 4 would be 8 if you had one, button 5 would be 16, 6 would be 32 etc. this is so you can check for combinations of buttons. so if you want to see if button 1 AND 2 are being pressed, you can use 3, which is 1+2. button 1 and 3 would be 5, which is 1+4.
if you just want to check for a button and don't want other buttons to interfere with it, you can do this:
mc=mouseclick()
if mc && 1
`this works if left button is pushed no matter what other buttons are pushed
endif
if mc && 4
`same here, except for hte scroll wheel button
endif
stop looking at me!