what games are they? some games have to be changed at the command line, in a config file, and others don't support other resolutions at all. personaly, if it's not a command line or config file i usualy just crank the FSAA and call it a day.
older games like these make me miss my Kyro a bit. many only support 16bit color, but the Kyro removes most of the banding you would expect.