That is the native resolution of my 22 inch widescreen monitor. I run GC2:DL/DA at 1600 x 900 Windowed (not fullscreen) with no problems.

I just tried that. Now it closes immediately. What are your [Video] settings? Here's what I just tried:

[Video]
DisplayWidth=1680
DisplayHeight=1050
ColorDepth=32
Fullscreen=1
HardwareMouseCursor=0
Multisample=4
Brightness=50
Contrast=50
AmbientLight=25
Resolution=0

I, too, can play in 1680 x 1050 on my 20" widescreen with no problems. My drivers (ATI) are up-to-date as of a week ago, too -- be sure to check that.

Even though I can play in 1680 x 1050, though, I still set it to run in 1400 x 1050, because widescreen resolution stretches out some images in the game (such as aliens' portraits when they're speaking to you), which I find highly annoying.

It is possible to set your graphics card so that it doesn't automatically stretch an image to fit your monitor -- that's what I do, and it gives me a normal 1400 x 1050 with a black bar of unused space on either side. If nothing else works, you might want to try that.

Ok, the immediate close was because the other version didn't shut down correctly. I killed it in task manager, here's the debug.err log:

Debug Message: Version v1.50x3 Dark Avatar last updated on: Mon Mar 12 18:37:34 2007
Debug Message: Checking DX Version.
Debug Message: *********DXDiag info follows.*********
System Info
Time: 5/27/2007, 22:30:32
DirectX Version: DirectX 9.0c (4.09.0000.0904)
Operating System: Windows XP Professional (5.1, Build 2600) Service Pack 2 (2600.xpsp.051011-1528)
Languages: English (Regional Setting: English)
BIOS: Phoenix ROM BIOS PLUS Version 1.10 A02
Processor: Intel(R) Pentium(R) M processor 2.00GHz
Physical Memory: 2048MB RAM
Page File: 1248MB used, 2692MB available
Windows Dir: C:\WINDOWS


Display Info
Display device 1:
Device Name: \\.\DISPLAY1
Card Name: RADEON X600 Series
Manufacturer: ATI Technologies Inc.
Chip Type: ATI MOBILITY RADEON X600 (0x3150)
DAC Type: Internal DAC(400MHz)
Key Device: Enum\PCI\VEN_1002&DEV_3150&SUBSYS_20021028&REV_00
Display Memory: 128.0 MB
Current Display Mode: 1680 x 1050 (32 bit) (60Hz)
Monitor Name: SyncMaster 204T/204Ts/204B,SyncMaster Magic CX201Ts(Analog)
Monitor Max Resolution: 1600,1200
Driver Name: ati2dvag.dll
Driver Version: 6.14.0010.6606
Driver Date: 3/21/2006 23:56:42
DirectX Acceleration Enabled: Yes



Sound info
Sound device 1:
Description: SigmaTel C-Major Audio
Default Sound Playback: Yes
Default Voice Playback: Yes
Hardware ID: PCI\VEN_8086&DEV_266E&SUBSYS_01861028&REV_03
Manufacturer ID: 1
Product ID: 100
Driver Name: STAC97.sys
Provider: SigmaTel
Driver Version: 5.10.4243.0000
Driver Date: 9/15/2004 13:53:12
Type: WDM
Other Drivers:
Acceleration Level: 3
Cap Flags: 0
Min/Max Sample Rate: 0, 0



Debug Message: *********END dxdiag info.*********
Debug Message: Entering WinMain
Debug Message: ******* Starting Game Shell *******
Debug Message: Going Fullscreen
Debug Message: Preparing to change display settings.
Debug Message: Using multilsample setting: D3DMULTISAMPLE_4_SAMPLES
Debug Message: Could not create the render device using default format. Switching to 16bit
Debug Message: Using multilsample setting: D3DMULTISAMPLE_NONE
Debug Message: Could not create the render device.
Debug Message: InitializeDirect3D Failed.
Debug Message: Now Fullscreen
Debug Message: Shell initialization complete
Debug Message: GalCiv2 is activated.

(At this point, it sits there with a dark square in the top left corner, until I kill it in the task manager.)

When I change my windows resolution to something other than 1680x1050, it loads just fine.