I think you'll need an AppleScript OSAX, such as
Jon's Commands, to change screen resolutions. The command
"screen list" is what you're looking for, me thinks.
Once upon a time, long before there was an AppleScript, i had a neat little piece of software called Switch-A-Roo, which used a hot-key to switch between two preset monitor settings. There may be other non-AppleScript solutions running around too which you might consider.
[ 01-13-2002: Message edited by: Rainy Day ]