IEEE 1394 (FireWire) compliant cards and cables make for good, cheap cluster High Speed Interconnects (HSI) within some strict confines. Since much of the traditional network gear (switches, routers, etc.) is not available under IP-over-FireWire, this standard lends itself most to directly connected hypercubes and similar constructs. By virtue of the fact that you are restricted to this arrangement, though, you can make some network configuration refinements that ameliorate some of the shortcomings of this implementation. Many operating systems tuned for clustering already support an implementation of IP-over-FireWire, and most of these are coming into compliance with the applicable standards specifications, including RFC 2734, IPv4 over IEEE 1394.