Canonical's Bryce Harrington has pushed a new unreleased ATI Catalyst driver into the Ubuntu 9.04 repository, which is compatible with X Server 1.6. This unreleased version is part of the fglrx 8.60 release stream and is likely based on Catalyst 9.4, which will not be released to the general public until next month.
"AMD delivered their xserver 1.6 enabled fglrx to me today for Jaunty. It built/installed/booted fine, and XSmoke didn't show any glitches. I've packaged it into fglrx-installer and uploaded, Bryce had announced on the Ubuntu-X mailing list. This package can now be found in the Ubuntu Jaunty repository.
This X Server 1.6 supportive driver is not compatible with R300-500 graphics processors, since that support has been dropped beginning with Catalyst 9.3. While this new beta Catalyst driver is out there now, do not be surprised if it happens to "disappear" from the Jaunty repository very soon.