Its actually very close now - pretty much as it was originally, but exactly as I wanted it in everything apart from IE6.
And I should probably say that I can't take credit for the design - I've just been approached to maintain the site, and maybe give it a refresh at some point. The original was in asp.net, which I'm not familiar with, so have been trying to recreate it in HTML / CSS.
I have tried to tidy a few things up thought - the right hand panel was all screwed in IE6 in the original too.