I have looked for this - but couldn't find an answer:
Has the full Vegas - or is there somewhere in my VMS Platinum - a "smart rendering" function??
I think of a possibility that when you have changed just a few frames, text or clips in a 20 minutes video, that you then should not have to use nearly 2-3 hours to render it all over again..
I do not even know if this wish is possible to do technically... but if it were - it would be a great feature (... at least until we get quad or more CPU's in near future :-)