how you should test your site with multiple browsers. You will found out that the most problems comes from Internet Explorer rendering of sites. Internet Explorer tends not to follow the W3C web standards for browser rendering. Yes I know you can put few on your system but there is a huge rendering gap between Internet Explorer 6 and 7. So how you want to test using IE6 and IE7 in the same machine. Well you can't Install all of them together cause they are using same DLL names and libraries. Technology has the advantage to give solutions in this situations.