My company regularly works on public facing websites, and as such it is imperative we test the sites we create with most common browsers. Naturally that means at least Internet Explorer, FireFox, Safari, and Opera. With the last three we just download and install om some test (virtual) machine. With IE however this is somewhat more complicated (although not impossible to run different versions of IE side by side. However, Microsoft provides a set of Virtual PC images known as the Internet Explorer Application Compatibility VPC Image. These images enable you to test different versions of IE on different versions of Windows. These images have a limited lifetime (between 1-4 months), so you'll have to download a new set on a regular basis, but other than that this is really handy. The following configurations are available:

• Windows XP SP3 with IE6
• Windows XP SP3 with IE7
• Windows XP SP3 with IE8
• Windows Vista with IE7
• Windows Vista with IE8

Unfortunately these configurations are all en-US, so if you want to test with say a Dutch version of Windows, you'll have to create your own images (which is what my company has done, even for en-US).