BOB YOU ROCK!!
I was having the same issue w/ a 1/2 hour HD B-Roll sequence (All footage 23.98 and FCP settings 10- bit HD 23.98). Having just installed FCS2, I had not looked at my RT settings. I spent half a day banging my head against the wall while ETT ate up all my drive space trying to render this monster.
Thanks again and Long Live The Cow!