xorg open driver and ati card Radeon 9200 agp

[Valter Giovannetti]

Hi.
Excuse me for my bad english!
I am a newcomer to Ubuntu and Italian!

On my computer I have an ATI Radeon 9200 AGP- RV280 chip.
The Operating Systems are: Windows XP and Ubuntu 11.04.
In WindowsXP all work ok.
Everything works fine with Ubuntu, 3D acceleration, if I use the VGA output.
Apart from the top rows in windows, when I move.
But the DVI output does not work well, if I try to move, enlarge a 
window, the monitor turns off and on again.
As if the video signal disappear.
I searched various forums how to fix the problem, but nobody could help me.
By installing the proprietary driver, present in the repositories, 
everything works fine, but 3D acceleration vanishes.
Can you helpme?
Thank you.