Hi kkmic, wpa_supplicant can also authenticate with wep encryption or with none - theres a GUI you can use or you can directly edit /etc/wpa_supplicant.conf, the configuration required in /etc/rc.d/rc.inet1.conf is something like this:
WLAN_WPA_OPTS="-dwext -iwlan0 -c/etc/wpa_supplicant.conf"
the -dwext is driver=wext
-iwlan0 is interface=wlano
the GUI tool is call wpa_gui, I'm pretty sure its either in slackware or in the slackbuilds repository. Good luck with it. As an aside I haven't used wicd so I cannot compare the two.
If you do decide to use wpa_supplicant the man page will tell you how to complete your /etc/wpa_supplicant.conf file (try