I have compiled and installed Dillo 2.0 in my Linux virtual machine. I have installed this because Netscape 4 is completely dead and it looks to be a reasonable browser for people living in their parents' basement still using a 486 to go online. This, along with IE 6 (20% market share and I will continue to support it until there is confirmed under 2% market share, probably around 2012 or so), are the "lowest common denominator" browsers I test my websites against.
All my websites are attractive in IE6 and readable in Dillo.
If your computer is a Pentium II or better with 64 megs of ram, use Opera 9, which supports modern CSS, passes the Acid 2 test, and is the most lightweight browser usable on today's internet.