Immersive Virtual Environments offer several new and exciting methods of interacting with computer systems. Virtual Reality systems provide users with a wealth of sensory information that can help us understand difficult visualization problems. The wealth of information and the variety of interaction tasks requires careful design of user interaction methods. At present, interaction in Immersive Environments is often performed through functionally overloaded input devices or through custom 2D and 3D simulated interfaces. The simulated interfaces might include virtual windowing systems, simulated information displays or visual menus. In many cases the custom virtual interfaces are placed between the user and the virtual environment data, occluding the user's view of the virtual world. The placement of projection surfaces around the user in Immersive Projection Technology systems allows the integration of real world interaction devices. One device we want to use in an IPT system is a palmtop computer. Palmtop computers can facilitate interactions with large amounts of data, alphanumeric information, or abstract operations that do not map well to current VR interaction methods. This research effort discusses the potential uses of a palmtop interaction system to reduce function overload and present familiar 2D and 3D interfaces to the user. This thesis overviews the design and usability testing of a palmtop interaction system for projection based VR systems. The discussion will include an overview of our software system; the Java based Interface to the Virtual Environment (JAIVE). The thesis highlights the system's usability design considerations, which include, consistent operation, task organization, and customizability. The thesis also addresses the use of Java[Superscript Tm] technology to ensure cross platform appearance and operation, to accommodate the development and integration of new interaction types, and to provide compatibility with new palmtop computing devices. We also identify potential applications of the interaction device and identify future directions for the project including spatial awareness and adaptive user interface techniques.