IMPS/2 is usually a safe choice. As far as getting the scroll wheel to work, confirm that in the mouse section of your XF86Config or xorg.conf file, there is a line that looks like this
Code:
Option "ZAxisMapping" "4 5"
Getting the scroll wheel to work is a very common issue, and additional information can be found by doing a quick search here at LQ. Good luck with it and Welcome to LQ! -- J.W.