I created an inner shadow for a div as in the following css code:
.gil_Help_ContentArea {
width: 300px;
height: 200px;
margin: 5px 0 0 0;
pad
At current (November 2011) it does not appear that anyone has developed a polyfill for IE8 or IE7 to do what you want. See, for instance, CSS3PIE (https://github.com/lojjic/PIE/issues/3) which has box-shadow support but does not support the inset flag.
Your best (only?) option is to create an image to use as the background for the element. This is, obviously, not a great solution.
(Also, to help you and others find other useful polyfills, here's a possibly useful link: https://github.com/Modernizr/Modernizr/wiki/HTML5-Cross-Browser-Polyfills)