This assumes that you're using conditional comments on the html tag to define classes for certain versions of IE. This technique was originally proposed by Paul Irish and refined in the HTML5 Boilerplate to something like this:
<!--[if lt IE 7]> <html class="no-js lt-ie9 lt-ie8 lt-ie7" lang="en"> <![endif]-->
<!--[if IE 7]> <html class="no-js lt-ie9 lt-ie8" lang="en"> <![endif]-->
<!--[if IE 8]> <html class="no-js lt-ie9" lang="en"> <![endif]-->
<!--[if gt IE 8]><!--> <html class="no-js" lang="en"> <!--<![endif]-->
You can omit the "no-js" class if you aren't using Modernizr, and feel free to remove or tweak the conditional comments to suit the versions of IE that actua