It appears that if you want to get the most out of networks that run at speeds higher than 10Mbps, you'd better have a fairly up-to-date machine. Our not-so-controlled experiment showed we needed two machines with processor speeds over 733MHz to get at least 50Mbps network throughput for both send and receive conditions.
If you're using a laptop / notebook computer on an Ethernet network, either get one with a built-in 10/100 Ethernet adapter, or make sure that you get a CardBus adapter. PC card adapters may be less expensive, but their 16 bit bus interface will definitely limit your networking throughput.
Although our experiments were done with Ethernet adapters, other testing we've done with 802.11a wireless adapters indicates a similar relationship between processor speed and throughput. So if you want to get the most out of 802.11a's higher networking speeds, you won't be able to use any of those $500 notebook close-out specials that look soooo tempting.