The Virtual Interface Architecture (VIA) is an emerging standard for low-latency, high-bandwidth, user-level communication designed to achieve high performance by minimizing data copying and kernel/user transitions. Currently very few network controllers provide VIA support, and the current specification for VIA does not include multicast, a useful mechanism for distributed applications. This thesis tests two ideas by experiment. Whether a software implementation of VIA can provide useful performance enhancement, and whether multicast support can be incorporated into VIA with tangible benefit. I designed a Windows NT driver software implementation of VIA for Gigabit Ethernet that achieved an average of 57% lower latency than Ethernet (UDP) for messages of one to 64K bytes. These low-level benefits translated to a reduction in execution time of 10--14% over UDP for several distributed applications, and with multicast, an additional reduction of 1% to 15%. We conclude that multicast support would be a useful extension to the VIA specification that could be added without difficulty.