In order to get the best results you need to define your DTD!
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
Also if you are using CSS it is a good idea to set all margins and padding to 0 and then define the element styles manually.
Code:
* { margin: 0; padding: 0; }