@suphiceto
for n900 the name of the wirles card is wlan0
example: airodump-ng wlan0
you need a bssid and a station ( the router and the pc conected to the router) if you dont have a pc conected you will not be able to capute data pack)
this is a example
CH 9 ][ Elapsed: 8 mins ][ 2007-03-21 19:25

BSSID PWR RXQ Beacons #Data, #/s CH MB ENC CIPHER AUTH ESSID

00:14:6C:7E:40:80 42 100 5240 178307 338 9 54 WEP WEP teddy

BSSID STATION PWR Lost Packets Probes

00:14:6C:7E:40:80 00:0F:B5:88:AC:82 42 0 183782

first is the router and station is the pc conected to taht router. ( at the moment the injection is not working, and you need a pc conected )