chromus:
Are you saying that if I adjust those values to match the pins for the mega (50-52) or (50-53) it should work?
Rather I'm saying if you don't change it, it WON'T work 
Certainly worth trying, though there may be something else too.
chromus:
A few things about Arduino irritate me including the forward/backward compatibility issues, but this isn't the place to grumble about things.
This incompatibility isn't Arduino's fault, it's all on the EtherShield library. Most people don't write their libraries to be Mega-compatible. But hey, it's free code.