/etc/network/interfaces

The manpage for this Debian configuration file is man 5 interfaces, see also man wireless and /usr/share/doc/wireless-tools/README.Debian. For resolvconf options (dns-nameservers, etc.) see also man resolvconf.

See this two pages: wpa_supplicant in Debian 6.0 and How To Use wpasupplicant.

With this configuration the WiFi connection will be not managed by NetworkManager:

auto wlan0
iface wlan0 inet static
        address 10.0.0.166
        netmask 255.255.255.0
        gateway 10.0.0.189
        dns-nameservers 62.48.51.6 151.99.125.2
        wpa-ssid MyESSID
        wpa-psk MyWPASecret

auto eth1
iface eth1 inet static
        address 192.168.0.191
        netmask 255.255.255.0
        gateway 192.168.0.249
        dns-nameservers 62.48.51.6 8.8.8.8
        wireless-essid MyESSID
        wireless-mode Managed
        wireless-key off