The enhanced ati.2 X driver created by the GATOS http://gatos.sourceforge.net
project offers some support for TV-out, but only in its "experimental" version, available through CVS. There have been reports from people who say they have made this driver work with one or another ATI card. For example, Bruce Markey mailto:firstname.lastname@example.org writes (on the mythtv-users mailing list): "I got this to work. You can quote me on that. I've used TV-out on several models of ATI cards both All-In-Wonder and regular cards with TV-out." See the "Adventurous Setup" section of http://gatos.sourceforge.net/watching_tv.php
for details. Also see http://www.retinalburn.net/linux/tvout.html
for more information.