Please see my comment to the question.
Even though you can always contain fluid-layout elements in the fixed-layout page (which of course would keep the whole design predominantly fixed layout), the attempt to contain fixed-layout elements in the fluid-layout design would anyway break the layout in case if the browser window sizes less then some of your fixed elements. So, even though it would be possible, it can defeat the purpose of such work. If you want to make the design fluid, you should try to keep all block elements to fluid design of their inner HTML.
Please see also my past answers with some links:
Webpage screen resolution (Cross Browser\Cross Platform) problem[
^],
To Get Screen resolution[
^].
—SA