Aspx pages within aspx pages.

Hi all, I have a problem I am not sure how to fix, I have an aspx page and in the html section of this page 4 other aspx pages are included; these make up the 4 sections of the page (Header, Navigation, Main and Right Margin(which can hold boxes with menu sections or just plain text)). when I include these files the system says only one <%@ page tag allowed per page. This means I cannot have CodeBehind for each section of the page and that is where the problem lays. when I try to reference a variable in the main form with "<%=id%>" it says I need to declare the variable. I have put the variable into the Global.asax file, but this makes no difference. I would appreciate any help with this very frustrating problem.