One of the most useful bits of kit I have installed is IE tester. This lets you view websites as rendered in Internet explorer versions 5.5 to 8. There is now a new version that includes the IE 9 preview platform, so you can test what your websites will look like in all versions of IE from 5.5 to 9. And whats more, its free! I recommend you download it, and if you like it and use it a lot, donate some money to the developer for the great bit of kit that they've developed.