Configured? The conf file is /etc/conf.d/net. You can setup your cards and how they act in there.
If you mean make sure the cards actually "startup" during the bootprocess then you'll have to add the appropriate net services to the default runlevel:
rc-update add net.eth0 default
rc-update add net.wlan0 default
Not sure if its called 'net.wlan0' though so check out the contents of /etc/init.d to see what its called.