I demoed it with my 7600GT &
AFAIK it works till 800x600, nvidia driver has an option to "center the output" instead of stretching.
6600 should support 1440 resolution, actually all nvida drivers have the capability to auto detect the wide screen on the 1st boot, u wont see 1440x900 at present monitor configuration, but the moment u connect it will chnage to 1440, if u have disabled the auto option then u can set custom resolution in the nvidia driver & save it.