Creating your own skin, or design template for IPB requires a bit of HTML and a lot of CSS knowledge. However, by building your own custom skin, you can completely customize the look and feel of your forum.
There are a lot of tutorials on Google about how to make a skin on Invision Power Board like:
http://www.smartestcomputing.us.com/forum/132-invision-power-board-3-ipb-3-skinning-and-editing/