If you go into your control panel, down at the bottom there should be an option for "Edit Templates". There you will find all the templates for every possible screen. Look for the one called "forumdisplay" and edit the HTML to your liking.

If you want to create multiple styles per forum, so each forum has a different style, you would create a new template for each style that you want, calling it something different. Then in Forum Options you can specify which templates that forum should use. So if you created Template A for Forum 1, you would select Forum 1, and speciy Template A as the template for that forum.

There is no hack involved; the templates are a standard feature in this software.

-jim