Make sure you have DHCP enabled on the Pismo in the TCP/IP control panel. Remember that you have have to close the TCP/IP control panel in order to save changes, so each time you try something, be sure to close the window. Also, it sometimes helps to restart after closing and saving that window.

Another thing that popped to mind was a crossover cable. You should be able to use an ordinary Ethernet cable with these machines, but theoretically there should be a hub or switch in between with regular cables. You might try hooking it up this way if possible or using a crossover cable to make it more reliable.