@blebbens It's been a while. But if I remeber it correctly you have to set #define SOFTSPI in MyConfig.h too. Don't forget to comment it back when you're compiling a sketch for a node.
My router uses DHCP as well. But I can assign a static IP in the sketch. Shouldn't be a problem.
I'm not sure, but I think the arduino can't handle DHCP, it's a really simple ethernet card. So you need to assign an IP in the sketch.