Microsoft Internet Explorer Doesn't follow standars so they have some code that other browsers don't...
As a web designer it is hard for me to create a site that displays exactly in every browser... So most people like me had decided to for what most people uses, IE. I personaly desgin all sites for perfect view in IE6 because a can't be coding for every single browser...
Sadly every browser has it's "stadars", the W3C sould force them to stick to one coding and help designers (and users) to have a more pleacent surf...
I like Opera, is one of the more sticked to W3C and is fast, Firefox has a lot of diferences with every browser (but mozilla of curse).
I hope some day every body (IE, NS, FireFox, Mozilla) make a deal and stick to stardard coding (HTML and CSS).
Some day... it is possible!!