including an XML file into another XML file

[ss596]

Hi all,
Feel stuck here.
I've broken my XML file into 3 parts. (The header, content and footer).
I assemble these XML files by putting the following statement in the beginning of the document main.xml

<?xml version="1.0"?>
<?xml-stylesheet type="text/xsl" href="convertToXHTML.xsl"?>
<!DOCTYPE cd_page [
<!ENTITY header SYSTEM "header.xml">
<!ENTITY content SYSTEM "content.xml">
<!ENTITY footer SYSTEM "footer.xml">
]>
and put &header; ,&footer; and &content; in main.xml file where ever I need these blocks inserted.

This main.xml file is linked to an XSL file which outputs XHTML.
When I open main.xml in internet explorer, it is perfectly converted to XHTML but it does not work on firefox.
So for compatibility with all browsers, I want to do the conversion on the server side and send XHTML output to the browser.
When I convert it on the server side using java servlets and XALAN API it seems XALAN doesn't support the assembly of the xml blocks in this way (i.e using <!ENTITY) .
Are there any other methods/approaches of assembling XML blocks. I can test them with XALAN to see wether they are supported or not?