transparency
Transparency using png images
Transparency using PNG background images that have an alpha transparency generally work better than transparency effects using the CSS effects
The catch is that internet explorer does not really like alpha channel PNG's and does not render the transparency without an extra filter or a transparent GIF like in this example, too bad it makes the text look ugly.
Download the attached CSS file to see how it is done.
CSS transparency without images
A transparency effect using only CSS, but unfortunately it has some drawbacks. View the source for how it's done.