Thanks for your reply and all the others-- the suggestions so far have been really helpful.
I wish I could provide more specifics about the setup in the lab, but since I've yet to do any work there, I actually don't know what platform I'll be running this on.
cjf, to clarify what I mean by screen, I need to fill the entire monitor with one background color, and write words to random spots on it in another color. Preferably this could be done without displaying any of the usual window-dressing (title bar and close buttons), so a browser-based solution does not really appeal. The idea is that the only thing the subject can focus on is the words that I present them, so really I'm basically just looking to turn the entire monitor white and print black text to different points within that big white backdrop.
Hope this makes sense and helps to clarify my needs, thanks again for all the feedback so far,