Fixed Top Menu

[www.sixtiesradio.co.uk]

Hi,

I have a site that works with frames, but I want to update if possible to
CSS.

The top section has the menu, and I have it so that clicking on a link in
the top section loads the required page in the bottom section, leaving the
menu fixed.

Can I do this using CSS? I can recreate the original index.htm page, but I
don't know how to encode the links so that only the bottom section is
changed rather than the whole page.

TIA