[BallisticWookie]

The higher the resolution you put your monitor at the lower the refresh rate you will get. Most monitors these days, 19+ inch flatscreen ones that can go up to resolutions of 1600x1200 can only do refresh rates of 60 - 75Hz.
The quality of your monitor and power of your graphics card are the most important things to look at when this problem arises. If you want higher refresh rates, use lower monitor resolutions. And, as Intrested pointed out, dont go spastic with this sort of thing, going to higher can cause damage to your monitor.