Problem with iMac mouse. No rotating


Few days ago I bought a new iMac Intel 10.6.7 64 bit with cordless keyboard and mouse… I have try everything but I can not rotate my Blender object with the mouse.
Do you know how to do. I dont have that problem with my old mouse .
thanks in advance

File / User preferences / Input, select “emulate 3 button mouse” tickbox

Thank you Richard. This work perfect.