I had the same issue. I wanted to include the same header and footer from the rest of my site, and wrap that around WWF. My header and footer had their own CSS associated with them. I just combined the CSS from my website with the CSS from Web Wiz Forums to get both. It worked out fine.
Note: When you combine the two, you may need to make sure that WWF CSS tags and your CSS tags do not conflict (i.e. your classes can't have the same name as WWF classes). I did have some conflicts when I first combined the two and had to tweak it to work as I intended it. But the results were wonderful. The average user can't even tell the difference between the forum and the rest of the website (unless you knew what to look for, of course). 