Halo 2 widescreen resolutions

I just started to hate microsoft even more. How do they manage to screw up Halo 2 more than Halo 1? I can't get it running in any normal widescreen resolution. In full screen mode I can only pick 800X600, 1024X768, and 1280X1024. In windowed, there are much more resolutions and the closest one to what I want is 1280X720, but it looks retarded in windowed mode. My monitors native resolution is 1440X900, but according to the wide screen gaming forum that resolution is completely unsupported. If 1440X900 is impossible, at least 1280X800 would be okay. I've tried adding the -vidmode 1440,900 and 1280X800 to the shortcut but that made no difference. I have an XFX 8600 GT XXX and an HP w1907 monitor. I'm running the game in windows XP using the loader.exe thingy.