You don't need "iwlist wlan0 scan"; you do need the other two however. The iwlist command will just give a printout of wireless access points and ad hoc wireless networks in range. You already know the essid of the wireless access point you want to hook up to so the iwlist command is unnecessary.
In non-debian distros you would just put these two lines at the end of the init script, /etc/rc.d/rc.local:
Code:
iwconfig wlan0 essid FON_Olympic
dhclient wlan0
Since mepis is debian based, rc.local may not exists. Check and post back if that's the case.