Switch Internet Explorer 6.0 to standard-compliant mode – level 200

It’s very easy to have IE render your web pages using current web
standards, but IE operates in “quirks” mode quite a bit, but it depends
on the web author.  If you are using ASP.NET 1.1 with VS 2003,
then this doctype is added for you automatically:
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”>
If you leave this, IE will not render your page using web
standards.  The problem is that the full Url to the DTD is not
included.

To switch IE 6 to standards-mode, change the Doctype to this:
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN” “http://www.w3.org/TR/html4/loose.dtd”>

This is the minimum you should do to every page you create with
ASP.NET.  There are other doctypes you should use for other
reasons, but at least change the Doctype to make IE render in
standards-mode.

Here’s a page from Microsoft that explains this more.