The page referenced in the URL has "color: transparent" in the table that holds the main text content. When selected in Vista (e.g., with Select All), the text is shown in inverted colors: white text on blue background. When selected in MacOS 10.5, the text is shown as transparent text on blue.
Looks like the page I referenced in comment 1 (http://www.religioustolerance.org/taoism.htm, removed because it's no longer applicable) already fixed their HTML. The test case Jesse put in bug 430606 should work: data:text/html,<p style="color: transparent;">Text</p>