CSS3 PIE is a .htc file that faithfully recreates css3 styling in early versions of internet explorer. Simply adding "behavior: url(path/to/PIE.htc);" at the end of the selectors scope that contains the CSS3 rule causes it to render correctly in otherwise unsupported versions of IE.
IE NetRenderer allows you to check how a website is rendered by Internet Explorer 9, 8, 7, 6 or 5.5, as seen from a high speed datacenter located in Germany. Just type in a URL in the field above and try it out - it's free!
There are several bugs in Internet Explorer that can be worked around by forcing "a layout" (an IE internal data structure) on an element (like, dimensional bug fixes and Holly hack). Most users are not aware of the implications of having "a layout" applied to an element. This document explains what happens when an element has a layout and what implications that has