I had the same problem with an Thinkpad T30 (ATI Radeon Mobility 7500). I had no freezes after switching to the vesa drivers. Maybe this is a short-time solution for you.
-- [dapper] xrandr freezes the system (radeon, MergedFB) https://launchpad.net/bugs/47775 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
