@Lynne: Why are you telling someone to install a mod when the feature already exists?
@OP: In each post there should be a bluish bar above the postbit, there you will find what date and time the thread was creeated.
I believe he wants the post creation date to be shown on the forumdisplay.php page. At least, that is what I assumed since I've seen that particular question asked so many times before.