Generally speaking DirectRT handles subliminal presentations very well and you can be up and running quite quickly. MediaLab is not built for such speed. Definitely check out:

Do I need both MediaLab and DirectRT?
www.empirisoft.com/support/showthread.php?t=15

Of course, there are limits to what you can do with any given hardware. I would suggest doing a general search on subliminal on the boards here to get a feel for the various issues that can come up, e.g.,

Why can I see my subliminal stimuli?
www.empirisoft.com/support/showthread.php?t=55