The following packages are involved in WiFi on the N900:
connui-conndlgs-wlan (provides dialogs for WiFi connectivity stuff)
connui-iapsettings-wlan (the wizzard for setting up a WiFi network)
icd2-network-wlan-config (provides some stuff connected to WiFi configs, no binaries in this package)
libicd-network-eap (eap module for icd2)
libicd-network-ipv4 (IP module for icd2)
libicd-network-wlan (WiFi module for icd2)
libicd-network-wps (wps module for icd2)
osso-wlan (WiFi daemon, open source)
osso-wlan-security (WiFi security daemon)
osso-wlan-dev (dbus interface for various WiFi things, open source)

Coming up soon is some info on the dbus calls and other external things used by some of these binaries.