Following humdinger’s directions, if you have tried and the network does not come up, it could be that your network card is still initializing. Try this in the UserBootscript:
( sleep 10; /bin/ifconfig /dev/net/YourWirelessDevice/0 join SSDNameOfYourWifi YourSecretPassword ) &
Choose the sleep in 10 second increments like… 10, 20, 30, etc…