Resolution won't stick!!! (Zoo Tycoon 2)

I have a problem. My monitor's native resolution is 1440x900, but the resolution in the game goes to 1280x1024 whenever I start it up. Meaning every time I start ZT2, I have to change the resolution to 1440x900 manually.

I've tried a few things to fix this problem and none have worked:

1. I edited the options.xml file to my resolution

2. I set the options.xml file to "read-only"

3. I DELETED the options.xml file and started over.

4. I reinstalled the game + expansions.

5. I reinstalled my graphics drivers (Nvidia 181.22)

My PC specs:

Intel C2D E6750 @ 3.2GHz
4GB DDR2-800 Ram
XFX 8800GT 512MB
Windows Vista 64 Bit
ZT2 + All expansions

HELP!!!