I cannot get the :nth-child selector to work with IE7/8.
Here is a working example of my code (that works in Chrome)
Below is the CSS and HTML I
That's because :nth-child isn't supported in IE7/IE8.
One solution to this problem would be to use Selectivizr.
"Selectivizr is a JavaScript utility that emulates CSS3 pseudo-classes and attribute selectors in Internet Explorer 6-8."
All you need to do is include the Selectivizr script and, if you aren't already using one, decide which JavaScript library you'd like to use (jQuery, Mootools etc.) and you will have support for the :nth-child selector (amongst various other pseudo-selectors/attribute selectors) in IE6 through to IE8.
Edit:
In reply to your comment, here's a quick tutorial showing you how to set up and use Selectivizr.