Creating Box To Appear To IE6 Or Below Users (Onload)

I'm looking to create a box that shows to IE6 users or lower, to tell them that my site does not render properly in the IE6 browser and that they should therefore upgrade to a newer version or alternative browser. Basically I would put whatever the code to show the box into these tags:

<!--[if lte IE 6]>
INSERT HERE
<![endif]-->

To enable it to only appear to IE6 or below users. Preferably when this box appeared, it would be nice if it could fade the page behind it. The box would also need buttons at the bottom that said "Ok, upgrade me" (this would load another window with links to alternative browsers) or "No thanks" (or "Close").