Sidechain Key-Input on a Noise Gate For 'Ducking FX'?????

[allears]

I am a Mac User and I would like to know of a gate Plug-in that would allow me to use an audio track as the key input in Live 5... Anyone?????

I do this all the time with the Noise Gate Plug in Logic 7 but wave yet to find an easy way to do this in Live.

Thanks in advance