question about VGA and VESA driver

[cckuo]

Dear X friends:
I edit the xorg.conf to force the Xorg using VESA driver, but the screen
displays improperly. Then I try to use VGA driver to light up the screen,
but the resolution always be 320x200, even I add the modeline option in
cofigure file. 
My questions are:
1. Should I add more options or set something else to let the VESA driver
work?
2. Or my monitor or HW cannot fit the vesa standard?
3. How could I set other modes in VGA driver?

Appreciate your help in advance.
cckuo
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