Farcry 2 Resolution Problem

[Tchesco]

Hi, I'm having trouble with changing the resolution in Far Cry 2. It only gives me these option as resolutions:
- 720x480
- 848x480
- 1280x720
- 1280x768
- 1280x1800
- 1360x768
- 1440x900
- 1680x1050

I've been running it on 2560x1600 with 4xAA with no problem, but I want to do some tests on 1600x1200, and 1280x1024 with 4x AA on, and AA off.

Here are the specs
Intel Core 2 Extreme @ 3.2 GHz
3 GB RAM
2x 4870x2 in Crossfire X
Windows Vista Ultimate 32 Bit

This is the only game that I've encountered this problem.