fiddle_dragon shared a great link to determine what the capabilities of IE6, Firefox 1.0, and Opera 8. It's at http://www.webdevout.net/browser-support and contains both a summary for HTML, CSS, and DOM as well as a detailed view for every little element. This is much better than most of the compability tables out there since a) it uses modern browsers, and b) goes into complete detail. Thanks Kethry!
In other news, I am upgrading perv.daft.com to the Sarge release of Debian. This means that I'm looking through changelogs from May 2005 to April 2002. There's a bit there… (EDIT: 698K, 17K lines)