I had problems like this in the past with purchased skins but I can't find the readme on how to fix it.
It's to do with your first forums category. If the ID of that was 1, your forum would look fine. If not, you have to edit the template and change 1 to the ID of your very first forum category.
I'll look in my old files again and if I see anything i'll let you know. I'm sure it's this problem your having.
This skin looks ace on one of my forums here:
www.meeting4fun.com
Modded slightly! If you hover over News and Information (My first category), it is ID 1