1st, get rid of the fixed width page... looks horrible on high rez screens.
Then, have left and right panels fixed width, and the centre panel fluid....for an example of what I mean, check my site: http://www.tenball.co.uk try it in different resolutions or try resizing the window, will show you what I mean...
Mmmm personally I wouldn't do it like that. If you're going to use the CMS, I'd make the site based around that, with the other bits and pieces integrated into it.