The refresh rate is related to the monitor and not to the video card. What you have done can cause problems to your monitor. The video card generates FPS (frames per second) and this rate is not constant and depends on the application that you are running.
I set the refresh rate to 75 Hz when my monitor is only 60 Hz.
To answer your thread title question about hurting your video card I have say no. This shouldn't even hurt your monitor as your screen will just be black. IE monitor doesn't work at the resolution. Many have a problem tho of getting your OS to start up without the black screen. For this you will need to press F8 and choice VGA mode. This will start windows XP in 800X600 which should work with your monitor.