What is it you're trying to get that header to do?
If you can go into detail about the problems you're having, I might be able to help you out.
Know that many rendering woes in IE6 and 7 (assuming that your problems are specific to an IE issue in the first place) can be solved by having a decent understanding of Trident's (the rendering engine in IE) proprietary and non-standard hasLayout mode. This is the definitive, most-helpful article on the web that I've ever seen around hasLayout is On Having Layout.
Many other issues you might be having might be self-helped through some of these articles found here at Position Is Everything:
