I had the same problem when I first tried it until reedo clued me in. When you post your next message, look up above the "post reply" box and find the little section that starts "Forum Rules:" (This one does (RULE) by the way, but you aren't allowed to use that expression on the bottom half of the board; if you do, a bunch of crusty Upright bassists will assume you're a BG player and start making fun of your name and your electric bass and just being mean in general). Anyway, at the bottom of that section, on the same line as "Posts", you'll see a blue underlined link for "Smilies". Just click on that and follow the instructions.
Just remember, no amount of smilies in any post will deflect the wrath of FUQHORN EDHORN and CRACKHOUSEKEY, so be careful what you post.
