My 20.1" LCD monitor isn't happy at resolutions lower than 640x480, I think you should stick to that or higher for compatibility reasons.
With my game project I'm planning to work at 800x600, and perhaps limiting the maximum resolution to 1024x768 (I'll try to support 640x480 too).
With my game project I'm planning to work at 800x600, and perhaps limiting the maximum resolution to 1024x768 (I'll try to support 640x480 too).