I am designing a web site and have gotten the overall design down good, but now I want to put up a BB using ph?

but now I want to add a forum using the phpBB (Prosilver) and still retain the look I have on the rest of my site, i.e. my own graphic at the top of the page and a links bar on the left side. I must be an idiot because I can't figure out how to do this even after mucho research. Our web site is www.pecosteaparty.org if you want to see what I'm trying to do. Right now, I've got the basic script installed but have no idea how to do the customizing I'm after, so I haven't opened it up to visitors (i.e. adding /index.php to the site address# Any help #or hope!) for me?