*Runs screaming from the building!*
You should be encouraging your users to NEVER use IE6, rather than trying to accommodate them. IE6 is the worst browser in the history of browsers – even Microsoft admits it’s very, very insecure.
Thus, I recommend using this plugin
To warn your IE6 users to upgrade to the news IE8.
While we all hate IE6 as CSS enthusiasts, its been discussed many times before but annoying them to upgrade is likely not going to do anything but push them away from your site. Most in IE6 are likely either quite computer-illiterate or (and more likely) stuck with IE6 at their job and cannot upgrade themselves.