We have designed a mobile -PDA-based- interface for real-time control of virtual characters in multiuser semi-immersive virtual environments - using a large rear-projection screen. The proof-of-concept implementation we present shows the potential of handheld devices as powerful interfaces to virtual reality applications. This technique eliminates the display of floating menus and other widgets over the simulation screen. A brief discussion on the advantages and disadvantages of using a handheld for 3D interaction is presented as well