In the case of CRT monitors it's a safe bet that they are all capable of 640x480 @ 60hz, as 60hz is a 'safe' setting that is usually used by default until changed.
As for TFT/LCD monitors, I'm not so sure. The screen on my iBook runs at 60hz, but I don't think all monitors of this type use 60hz as their native setting. Others will need to confirm this.
Having said all that, a lot of people are quite susceptible to the flicker you get at 60hz on a CRT monitor, myself included. As such, I generally don't play these games, as they soon start to give me a headache!
If you're programming for fun then stick with 60hz. If not, then have 60hz as default, but allow the user to change it somehow if they want to.
As for TFT/LCD monitors, I'm not so sure. The screen on my iBook runs at 60hz, but I don't think all monitors of this type use 60hz as their native setting. Others will need to confirm this.
Having said all that, a lot of people are quite susceptible to the flicker you get at 60hz on a CRT monitor, myself included. As such, I generally don't play these games, as they soon start to give me a headache!
If you're programming for fun then stick with 60hz. If not, then have 60hz as default, but allow the user to change it somehow if they want to.