To the untrained eye it's tough to notice, but it's worth knowing about. Most of the time, the monitor is the bottleneck when going to high refresh rates or resolutions. The important thing to do is make sure your monitor and video card have a good match for the refresh rates that you want in the resolution and color depth you want. There is no specific way to control the refresh rate in the original Windows 95. There were controls built into Windows NT to set it directly.
Refresh rates are also a function of the monitor.
Generally, I would suggest using the highest refresh rate that both your monitor and video card can support. Sometimes, however, high refresh rates will cause banding, or inconsistencies in your display. This is generally due to a substandard monitor cable or interference. These problems can be tough to track down, so if you can run at 90 Hz with some banding or 75 Hz with a nice clean picture, I'd go with 75 Hz. Pick the rate you want.