Modern high speed networks, such as ATM, can provide the bandwidth and the QoS guarantees to demanding real-time multimedia applications. However, overall performance of a networked multimedia application will greatly depend on the in-host data movement. Analyzing the characteristics and requirements of those applications, we came to several conclusions about the operation of the multimedia devices' drivers. We applied these conclusions in the design and implementation of a device driver for a multimedia teleconferencing system, based on IBM RS/6000 servers, running the AIX 3.2 operating system. Tracing the complete in-host data path, we found that though our device driver minimized the movement of data between the teleconferencing card and user main memory, the UDP/IP stack proved to be a cause of delay in the movement of data between user main memory and the network interface. (Also cross-referenced as UMIACS-TR-96-18)