I don't think your use of iFrames is appropriate for your site. You're building and styling the site the way things were done in 1996. Look around the web a bit and you'll not see many sites build the way yours is. iFrames are generally only used on an odd page or two where it helps to keep all the data in the one place.
eg http://thehamblintrust.org.uk/events.htm (this is a very old site)
see how it uses the iframe, and why it helps. But that's the only page with an iframe
Using them for general page and site layout is a long forgotten and generally disused technique. May it rest in peace.