Well, I finally -- being new to Linux/Unix -- have the ATI drivers properly installed. The slower graphical performance in Firefox is acceptable, so that's okay for the time being.
Blender 2.46 is now a lot faster... GREAT! But there's a problem: when the mouse cursor is in certain spots, the Blender window pops in and out of existence. For instance, if the cursor is down below the window is gone. When I then move it up a bit, it returns. When the cursor is in a too high position, window disappears, etc.
Any thoughts and solutions?