+1 for being a trackball user
My Marble Trackball, the middle mouse button is non-functional until I install the Logitech trackball software... Once installed, in that software you can "turn on" the middle mouse button functionality. (sucks i know as it should work by default).
[Added Note: in the logitech software you have to assign "middle mouse button" to the middle mouse button. Silly I know. haha]