The challenge with the box model is that Internet Explorer before version 7 didn't implement the box model correctly. When you put a width and padding on an element, Internet Explorer would subtract the padding from the width of the content.
This meant that pages that relied on the box model for layout would look different in IE and standards compliant browsers. Sometimes disastrously different.
If you must design for IE 6 or lower there are a few things you can do:
- Use style sheet switching to give IE a different style sheet than standards compliant browsers.
- Apply a box model hack to your style sheets.
- Not use padding on elements with a defined width. This can often solve the problem, and you can fake padding with nested elements.
- Not worry about it. As long as the pages look okay in both browsers, most people will never know that there are differences in a browser not of their choice.