Shamelessly stolen from antirice's page (in case he changes it, I don't want to lose it ;):

• Ever wanted to run more than one version (of IE) on your Windows box? Well, now you can. If you're a win nt/2000/xp user, you can use versions as far back as IE 3.0 for Win 3.1.
• Looking for a place where you can get those difficult-to-find out-of-date versions of browsers? Well, look no further. How far back do they have? How does Mosaic 0.6-BETA sound? (Note, it crashes like you wouldn't believe. 2b works pretty well and can even display PM. However, don't use the CB or it will crash. Btw, you also need to use File, Open URL to get it to work.)