Can't you just specify it as a custom resolution in Powerstrip? If you're using the shareware version, I know it won't save your cutom res and next time you boot, you're not in it anymore.
Personally, I'm looking at using an AIW 9800 when released, Powerstrip, and Win XP Pro and forcing a resolution of 1600 x 1024 (not supported by ATI drivers) for my widescreen monitor.