This won't work sadly. When the text appears the player will not move. And you will have to manually control the text. I do, however, think there is a script which allows you to do this. Try looking in the Custom Message Systems section of the Forum Script Listings.
EDIT: I may have misunderstood you. Do what bojjenclon said, but in an Autorun. This way you can't move while it's going on.
Peace,
Mundane