One really annoying facet of building websites is the fact that different browsers treat the same code in varied ways. What makes it worse is that you can't install multiple versions of the most popular browser on a single machine. Just last week we had developers jumping from machine to machine trying to iron out a code problem that occured in IE6 but not IE7.
I haven't tried this but thought someone might like to give it a go: an installer that installs multiple versions of IE.
Via CreativeBits