in reply to CGI header

I might be misunderstanding the question, but I believe I did something similar to what you might need a long time ago. I put all of my header code in to a separate file and called it when needed throughout my CGI.(multiple pages, forms, error pages, confirmation page ...) it acted more like a bread crumbing, but maybe this is what you are looking for? I second the use of Template::Toolkit, but this was writen before I was comforatble with it, and can an alernative if you are limited to what you can use.
My 'header'
sub displayHeader{ print <<DISPLAYINGHEADER; <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <!-- continue all of the junk you want to include in each page --> DISPLAYINGHEADER }

From there, my CGI required the displayHeader file and called it like so:
sub displayErrorPage{ &displayHeader; ... } sub displayConfirmationPage{ &displayHeader; print $cgi->p("Thank You"); ... }
The two functions above are entered based on the return value of a form validation subroutine (error checking form input).