Dark Messiah of Might and Magic
Find the following config file:
\Dark Messiah of Might and Magic\mm\cfg\config.cfg
Enter these key bindings into the config file:
bind "w" "cl_drawhud 0"
bind "q" "cl_drawhud 1"
Replace q and w with the keys of your choice.
The hud was not intelligently designed so it has to be re-enabled to switch weapons, but can be disabled again when not needed.