Trident Cyber 9525 - vesa driver

Hello

I use Linux on an old laptop and am having problems with the configuration of "xorg.conf"
My video card is a Trident Cyber 9525 and when I use the Trident driver, I have a problem with scrambled lines at the bottom of the screen.
Usually, in other linux distributions I fix this using the vesa driver.
In xorg.conf I change the line
Driver "trident"
By
Driver "vesa"
But on ubuntu 8.04, when I do this fix, when you start X, the screen is scrambled and blinking.
What should I do?

Thank you.

SOLVED: I just change xorg.conf with this line:

DefaultDepth 16
in Section "Screen".

Thanks.

How do you get to a terminal and then to xorg.conf to make changes?

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