I tried adding the forum button to the babylon theme using the info in the Working with Custom themes but the button still doesn't show up. I'm including the two requested files for assistance...thanks!
Try the attached files.
Also make sure that you have a '/Themes/babylon/images/english/forum.gif' button if you are using images. I believe that this topic (http://simpleportal.net/index.php?topic=713.0) has a 'Forum' button attached for that theme, if you need one.