How do you freeze or lock tracks in Logic 8 express

How do you freeze or lock tracks in Logic 8 express. My computer stops in some songs during playback and message says exceeded cpu. In garage band there was an easy to find "track lock" feature. The Logic manual seems to imply that freezing is what I want to do in Logic. I found the picture in the Logic manual but can not seem to find the buttons in the software program. Thanks