These instructions quoted from: http://www.ttlg.com/forums/showthread.php?t=101841
The following commands will turn off various parts of the HUD:
You can bind all of them to a single keypress by editing your user.ini file in Deus Ex's System folder as follows, using the minus key as an example:
Code: Minus=togglecrosshair|togglehitdisplay|togglecompass|toggleaugdisplay|toggleobjectbelt|toggleammodisplay Make sure you change all occurances of lines beginning with "Minus=" if more than one exists.
You can also enter them as standard commands at the ">" prompt, if you prefer.
I believe that means you can press the Talk button (default key T), remove "say" then type commands in game.
Screenshot showing the only remaining hud element, dialogue windows that pop up when an NPC is talking to the character.