Click on the Rolodex icon with the person next to it that's contained in every post or reply. That'll bring up the user's profile.

Or, go to the direct link:
http://www.flyertalk.com/forumcgi/ubbmisc.cgi?action=getbio&UserName=[UserName here.. for Names with Spaces, Replace the Space with a +]

Then there will be a link that says "Search: All posts by this registered user." The first 300 posts found by the system will display.