[Wayne Luke]

The easiest way to do this is to use what Microsoft calls "Conditional Comments". Internet Explorer is the only browser to use these constructs.

<!--[if IE 6]>
Special instructions for IE 6 here
<![endif]-->

If the user is using IE6 than it will include everything in the comment when processing the page.

You could also do something like:

<!--[if lt IE 7]>
Special instructions for IE 6 and earlier here
<![endif]-->

Doing a search on conditional comments will give more tutorials.