There is many of technologies that are not supported in IE 6,7,8 and even 9; such as rich text editing and faster Java script execution. some of these features supported on the new versions of IE but not supported in the older versions, like the curve edges for tables, buttons..etc (supported on IE 9 but not on IE 6)
Usually the end users would like to see the same UI over any browsers and the bad news is, there are some people working on the very old version of IE; IE 6 – I have no idea why they still using such browser.
on the other hand; the GOOD NEWS; There is plugin form Google Chrome, that you can install it on the old IE version and let Chrome handle rendering the websites just like if it is running under chrome. it will be look very good and execute the client side script in very efficient way. that would make the developer life much easier and get rid of having the headache of supporting multiple browsers with very old technologies like IE 6!
Installing this plugin will be very easy, it will be a matter of single click, to install this plugin, please use the below link to get into the downloadable area from Google Chrome!http://www.google.com/chromeframe?quickenable=true
Basically, this plugin will create a frame inside the IE and let Chrome rendering engine render the web page instead of the IE browser; that means whatever is supported on the LATEST chrome version will be there as well. it is like do a perfect union between IE and chrome to get the best of chrome inside the IE!