The original site design was probably tuned for some specific version of IE, taking advantage of that browser's quirks and errors. That's not a good way to make a web page. Try not to use tools which are highly tuned to a specific browser, but that generate good generic HTML and CSS. At the very least, try the completed page on a number of different browsers to see if it looks and acts reasonably well on a range of browsers. You may need to do some manual tweaking of HTML and CSS to get it to work well everywhere.