IE's Default CSS Values

Here is a CSS comparison chart. IE actually stores the CSS settings in the ever-so-dumb-place, the Registry. Another issue is whether the doctype of your application is using standards mode or quirks mode.

If it's using quirks mode, you're in trouble. Fixing things for non-IE issues will break IE issues etc. You will go insane.

TBH, I'd be surprised if IE6 actually used CSS internally for laying out the majority of HTML elements, so what you're looking for may not even exist.

The W3C have a sample stylesheet in the CSS2 spec (http://www.w3.org/TR/CSS2/sample.html) which "describes the typical formatting of all HTML 4.0 ([HTML40]) elements based on extensive research into current UA practice" - copying that into a stylesheet is probably the best you'll do.

While I don't think I've ever seen a list posted, the IE Developer Toolbar lets you poke around the computed styles of your various elements. Create a dummy page with each of the elements you're interested in, but no CSS, and mine out the values you need?