Pg. 83-84 in the 5.0 Reference Manual:Pro Tools can generate a midi note click track that follows the tempo set in either the Tempo Ruler or the Conductor track. This is not an audible signal. You must route this track to a midi device, or a Quicktime instrument.In the Midi menu, select Click Options and select the destination device under Output Device.Enable the Click track by selecting Click from the Midi menu or Transport window.Make sure the audio outputs of your midi device are routed into a mixer or an auxillary track in Pro Tools (via the Digidesign interface).