Yes, the issue is more complicated than the solution implies. More information on DOCTYPE switching and other code and standards related features in IE6 can be found in the document "CSS Enhancements in Internet Explorer 6" located at:
http://msdn.microsoft.com/library/default.asp?url=/workshop/author/css/overview/CSSEnhancements.asp
Many HTML tools, templates, and tutorials insert code at the top of HTML pages to precisely define the tagging system:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> ... etc.
Modern browsers (IE6, IE5 Mac, Netscape 6, Opera 6) will take the presence of this declaration as a clue to strictly interpret the HTML and CSS.
See a DOCTYPE element? Delete it. IE6 goes into "compatibility mode" and now interprets page code as if it were an earlier version. You are now IE6 ready.
This only buys you a little time and saves embarrassment. Your goal should be to create W3C validated code, which requires a DOCTYPE.