You do need a running TCP/IP stack such as Genesis, that can be found on the OS 3.9 CD. Best you configure a static IP for your A1200 in it.
As for the SetPrimDefault you need to specify your WEP key (after KEY) and your SSID (after SSID) in the startup-sequence.
Make sure to make an entry for the MC-11 in your router's MAC filter (in case you use it, that is). Try and ping around (router, other computers in your LAN, internet) with the command to be found in AmiTCP:bin (that comes with the TCP/IP stack). Unlike in Win, the pinging will stop only if you press CTRL-C.
