Xorg at 1920x1600 using vesa driver?

[Sebastiaan van Erk]

Hi all,

I just got a Dell E1705 (Inspiron 9400) which has an unsupported ATI 
RADEON MOBILITY X1400 graphics card. Personally I'm not really 
interested in all kinds of hardware acceleration etc., the only thing 
that matters to me is that I can use the 1920x1600 resolution.

In my Xorg.0.log the vesa driver says:

(II) VESA(0): Supported additional Video Mode:
(II) VESA(0): clock: 162.0 MHz Image Size: 367 x 230 mm
(II) VESA(0): h_active: 1920 h_sync: 1968 h_sync_end 2000 h_blank_end 
2160 h_border: 0
(II) VESA(0): v_active: 1200 v_sync: 1201 v_sync_end 1204 v_blanking: 
1250 v_border: 0

and a bit later:

(II) VESA(0): Total Memory: 256 64KB banks (16384kB)
(II) VESA(0): Monitor0: Using default hsync value of 75.00 kHz
(II) VESA(0): Monitor0: Using default vrefresh value of 60.00 Hz
(II) VESA(0): Not using mode "1920x1200" (no mode of this name)
(--) VESA(0): Virtual size is 1600x1200 (pitch 1600)

I tried playing around with the hsync and vrefresh values, and added a 
ModeLine for the 1920x1200 in the Monitor, e.g.:

    HorizSync 31.5-128.5
    VertRefresh 40-150
    ModeLine "1920x1200" 400 1920 1968 2000 2160 1200 1201 1204 1250

However, the message that there is no mode of the name "1920x1200" keeps 
appearing and it keeps using 1600x1200.
Does anybody know if it is possible to get this mode working with the 
vesa driver and how to go about it?

Thanks in advance!
Sebastiaan