IE 6 doesn’t live happily side by side with IE 7 or IE 8
To do compatibility testing of a web page I usually have to fire up a VPC and access the page from a browser instance inside that VPC (one VPC for IE6, another one for IE7, etc.)
Lately I’ve started using “SuperPreview”.
It plugs in to Expression Web and lets you choose what browser to preview your page in (IE 6/7/8, Firefox)
Very cool !