Hello! I wonder if anyone knows a way to connect an
wifi network from the console of mobile ... eh tested using
following commands I found on google

ifconfig wlan0 up
iwconfig wlan0 essid elnombredelaESSID
iwconfig wlan0 key lacontraseña

The problem arises when I try this:

dhclient wlan0

Which is finally connected to the network.

Anyone have any idea how I can get this??

You're pretty much on track.

As root...

ifconfig wlan0 up

To list out access points that can be seen from your N900...

iwlist wlan0 scan

To join an unencrypted network

iwconfig wlan0 essid "name of network"

If the network is encrypted, you need to enter the key in hex - you can use a calculator for that - a randomly googled calculator is here

You've made a mistake with the encryption key. It needs to befor an ASCII password, without the "s:" it interprets the key as HEX. These commands will only work for WEP encryption (which is very insecure btw, and can be cracked in just a few minutes with the right software installed). WPA/WPA2 requires something like wpa_supplicant to handle the encryption. The n900 doesn't have wpa_supplicant installed, but since it connects to WPA/WPA2 networks there must be some other mechanism in play, but I haven't worked out what that is yet.

If you want to connect to an already configured network you can follow the guide here.

EDIT: On second inspection; unless "ESSID" is actually part of the wireless network name (the ESSID) it shouldn't be tacked on the end of the network name.

If you want to connect to an already defined connection:

http://wiki.maemo.org/Phone_control and [Announce] Phone Control Script

tanks for the answers... but i can't get connect... there is a missing command that alow me to GET conect with the wifi essid... i use this comands...

ifconfig wlan0 up

iwlist wlan0 scan

iwconfig wlan0 essid "name of network"

but i didn't get connect... cause i need one more command but i don't now which one...