@Redrumloa:
It's a German forum, but they won't shoot you (or your friend) if you post a question in English:
http://forum-64.de/wbb2/They have a dedicated sub forum for RR-Net/Contiki (go to "Neue Hardware", then "RR-Net / Contiki") and there are some pretty experienced guys over there - including some that used said setup to connect their C64 to their LAN and bowse the net with Contiki.
