When you see a post, click on the screen name of the person who made the post. You'll get a new screen with information about that account -- on yours, upper left hand corner, it says, "Since Sept. 12, 2004".
Just click on their name at the bottom of their post. :)
BTW, I'm computer illiterate, too. FR has taught me a lot. Especially the "HTML Sandbox" here:
http://www.freerepublic.com/focus/f-news/938739/posts