Just to say that the nuelectronics ethershield do not work with the Arduino NG (I think it is the same for NG rev C) because of the SPI pb.
I managed to get it working after applying this hack http://www.eng.uah.edu/~jdw/avr/arduino_r13_mod.jpg
from this post http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1163734586
.(the cmd resistor stayed stuck 10 seconds on my hot iron but seems to work perfectly) 8-)
Thanks kg4wsv !!!
Another pb : the ethershield do not initialize correctly without the USB plugged (the jumper is on ext power and is well plugged : strange...)