conduit sounds like a fantastic plugin that give you real time keys plus they have a lot of great video tutorials on how to use it
it is giving you nodal compositing in motion
if you want free i have tried the primatte keyer in motion, take down the noise spill supressor and other paramter and then refine matte desity a tiny bit
then use a levels command and set to alpha and get contrasty alpha channel
then try a blur on the alpha channel if needed
then use a colour corrector to despill
if you have crap footage and it is dv then you need to be pretty brutal to the edge
if it is just bad contrast then try multiple keyers and use the mask tool in motion (its easy to keyframe with the record button)
also make sure you have progressive footage if you need to use compressor to get you there