If you want to properly test the websites that you build, you should really test them in as many of the common web browsers as possible. That much is obvious, what isnt so obvious is where to find older versions of the web browsers, so you can install them for testing.
My mate Darren just told me about this site that has archived most, if not all, of the web browsers that exist on all the different operating systems (including devices such as Set Top Boxes and PDA’s).
For example, most useful for me at present are these:
Here you can download every version of Microsoft Internet Explorer (32 Bit) and here you can download every version of Netscape Navigator (32 Bit).
Definetley one for the bookmarks.