First, do you need to show the SAME image multiple time at 120hz? If so, just show it one time and if you graphic card and monitor support 120hz, it will be refreshed like anything on your screen at 120hz...
If you talk about showing a video at 120hz, I don't know how to do that. You could try to play it faster by playing 120 frame per seconds but it will look like fast-forward... And anyway, most of users has screen of 60hz so they will never see 50% of your images...
Can you provide more information about what you are trying to achieve? I'll edit my answer if you give more information.