Only the last few posts show on your profile. Just post to a few innocuous ones like Cooking or Humor to move them down the list a bit.
If you click on a user's name in a forum thread or topic list, you can view the last 25 posts or the last 25 active threads he or she has participated in.
Then there is the History link next to each post. That appears to show a person's last 50 posts.
Google Search a username sometime. It gives you the same results, plus the option to view cached (older) pages.