Be careful using Compressor to output Mpeg2, there have been isssue with 2 Pass VBR, it looks like crap.
What works for me is to install the Mpeg2 Codec that come with DVD Studio 2 or some other application. Once that Codec is installed, you can export from FCP and choose that Mpeg2 Codec, configure the setting to 5.5 Mbit Target Rate and 7.5 Mbit Max Rate and make sure it is set to 2-Pass VBR.
that works well, looks good and you don’t have to figure out Compressor.
Kalagan