Here's how to enable them:
At the top of this page select "User CP". On the left side under "Settings and Options" pick "Edit Options". Scroll all the way to the bottom of the page where is says "Miscellaneous Options". Make sure that you have "Enhanced Interface" selected from the drop down menu. Hit "Save Changes" at the bottom of the page. Now when you select "Post Reply" at the bottom of a thread, you should see the different options above the box where you type your text. You can change the color, size, style of your text and there should be a white smiley face where you can select smilies.