export mixdown of several stereo tracks as one mono track

How can I select a few stereo tracks in STP and export them as a single mono track? either back to FCP or as a standalone file?

Thanks!

Processor 2 x 2.8 GHz Quad-Core Intel Xeon

Memory 32 GB 800 MHz DDR2 FB-DIMM

Graphics NVIDIA GeForce 8800 GT 512 MB

Software Mac OS X Lion 10.7.4 (11E53)

Final Cut Studio 7

Oops, i posted this in the wrong discussion group. can this be moved to STP?