Did you check the site using IE6? Almost all of your users will be using IE6 or 7 or Firefox.

IE6 will take some tweaking of your code to display properly. IE5? I wouldn't even bother but if you must design for it, you have your work cut out for you. If you're using CSS, try using a different style sheet for IE5 and probably 6. I use 2 - one for Firefox and IE7 and one for IE6.

You might need to clear your cache to see the updated pages.