FW: X resolution too low

[Brian Astill]

I think I have the same or a very similar problem.
I had a faulty Nvidia card and replaced it with an updated version 
Here is the spec:
Chipset GeForce FX 5200
Memory 128 MB
Bus Type AGP 8X
Memory Type DDR
Memory Bus 64-bit
Output DVI
Highlighted Features TV Out
Graphics Core 256-bit
Memory Interface 128-bit
Fill Rate 1 Billion Vertices Per Second
63 Million Pixels per Clock (peak)
4 Textures per Pixel
13 
RAMDACs 350 MHz

The Monitor is LG Flatron T910B, auto-detected correctly as:
(**) NV(0): Using gamma correction (1.0, 1.0, 1.0)
(II) NV(0): T910B: Using hsync range of 30.00-98.00 kHz
(II) NV(0): T910B: Using vrefresh range of 50.00-160.00 Hz
(II) NV(0): Clock range:  12.00 to 350.00 MHz

So - WHY can I go no higher than 1200x1-24, when the system is 
capable of 2048x1536?  I really want a "mere" 1600x1200.

Both XF86Config and xorg.conf list 1600x1200 as one of the "modes"

Help would be appreciated.  I'm using Dapper with KDE added.

-- 
Regards,
Brian