when you type iwconfig does your card show up in monitor mode?
You should see something like this where I bolded it:
ath1 IEEE 802.11g ESSID:""
Mode:Monitor Channel:0 Access Point: Not-Associated
Bit Rate:0 kb/s Tx-Power:19 dBm Sensitivity=0/3
Retry: off RTS thr: off Fragment thr: off
Encryption key: off
Power Management: off
Link Quality=16/94 Signal level=-77 dBm Noise level=-93 dBm
Rx invalid nwid: 0 Rx invalid crypt: 0 Rx invalid frag: 0
Tx excessive retries: 0 Invalid misc: 0 Missed beaco: 0



