As a rule, I go with adding classNames to the body tag via conditional comments as my preferred method to deal with cross-browser difficulties.
However, if that's out and if performance is not a concern, you can always give Dean Edwards's excellent IE7.js a try. It will parse and grok your stylesheet, picking out and implementing those unsupported selectors.
Beware that, as your stylesheets increase and size and complexity, the script's (and your site's) performance will suffer in IE6. However, in a lot of cases things should run just fine. Make sure to conditionally comment it in for IE6 and below and you'll be set.