CS4 works native with AVCHD - you don't need anything special to work with the format unless you have a computer that isn't powerful enough in which case an intermediate codec would come in handy.
one more question ...... how do you guys do pulldown removal to get to 24p?... do I put my footage in the timeline before I go to interpret footage or where should my footage be? and howcome I can't check on the pulldpwm removal box...