If you use a wpa network, you should use wpa_supplicant.conf. If you're using either WEP or no encryption (neither is recommended), then you can just have everything in rc.inet1.conf, but it is still recommended to use wpa_supplicant.conf. Using that, you can define multiple networks, which can be handy if it is a portable device like a laptop.
See the slackbook page on networking for more info.
http://alien.slackbook.org/dokuwiki/...wpa_encryption
