Hm - DirectRT can handle subliminal messages; however the output being used must be able to handle rendering each frame that quickly. For rendering images at a 120 Hz refresh rate, I would recommend the following monitor:
http://www.newegg.com/Product/Produc...82E16824001311

Common monitors will output at 60 Hz, meaning they will render at 60 frames a second, or rather (1000/60) 1 frame per 16.67 milliseconds. A monitor with a 120 Hz refresh rate similar to the one above will render at 120 frames a second, or (1000/120) 1 frame per 8.33 milliseconds.

DirectRT cannot create a video with the output you've noted; however it can run experiments at just about any timing resolution - as long as the monitor being used has a high enough refresh rate to handle the refresh rate required by your experiment. MediaLab is not capable of this, as it doesn't use the actual refresh rate of the monitor to specify when stimuli are drawn to the screen.