Hello. I must agree with the other two posts. A logo is a must, change the colors and (I'm not sure if it's possible with phpBB--never used it) but I think you should also include your site's navigation bar linking the BB back to your main web site.
Much like HTML Center, for example, they include the standard navbar, logo and search field at the top of the forum. This, in my opinion, "integrates" the forum into the rest of the site.
Just my two cents!
