Geeky computer question - How do I keep Internet Explorer 6 in Windows installed if I update Windows itself?

Okay, I’m not a fan of these questions, but I know a fair amount of web-designers/developers peruse this site. I need to make sure my newest project is rendering correctly in IE6 (Internet Explorer 6). So I loaded Windows XP in a virtual machine (on my Macbook.) Same as a fresh install on a Dell or something. I want to update to Service Pack 3, or whatever they are up to but keep IE6. Their info for the updates is so confusing! Thanks?