In Labview 6.1, use an Event Structure. Look at the Mouse Control Demo.vi and Draw Graph with Events.vi examples that shipped with LabView 6.1. From any Labview window, goto Help >> Find Examples >> Search >> Type a keyword to find, then enter Mouse.
The Draw Graph with Events.vi uses an Event Structure which can be used in many different applications. The Mouse Control Demo.vi uses a Mouse property of a Picture control. Most controls don't have Mouse properties, but Events can be used with any control.