As you all know there are a couple of differences in rendering your website in different browsers (Internet Explorer 6/ 7 / 8, FireFox 2 / 3, Opera and Safari).
You as front-end developer have the responsibility to make sure your webpages are supported for all browsers. Microsoft introduced “conditional commenting” as a sollution, but often you do not want to add in a whole CSS file to fix a single pixel. In these cases you need a “hack” in CSS to accomplish this.
Before I give the solution to your rendering differences in Internet Explorer, you need to understand these hacks should only be used when all other options are eliminated since they are mentioned as final solutions for tiny bugs.