If your card is Atheros, make sure you're using the correct drivers. Mine was working fine.
madwifi_a Atheros Linux madwifi-cvs
http://sourceforge.net/projects/madwifi/
Capture interface: 'athX'
Madwifi drivers in 802.11a-only mode.
madwifi_b Atheros Linux madwifi-cvs
http://sourceforge.net/projects/madwifi/
Capture interface: 'athX'
Madwifi drivers in 802.11b-only mode.
madwifi_g Atheros Linux madwifi-cvs
http://sourceforge.net/projects/madwifi/
Capture interface: 'athX'
Madwifi drivers in 802.11g-only mode. This will,
obviously, also see 11b networks.
madwifi_ab Atheros Linux madwifi-cvs
http://sourceforge.net/projects/madwifi/
Capture interface: 'athX'
Madwifi drivers in 802.11a and 802.11b combo mode. This
will seamlessly switch between bands during channel
hopping.
madwifi_ag Atheros Linux madwifi-cvs
http://sourceforge.net/projects/madwifi/
Capture interface: 'athX'
Madwifi drivers in 802.11a and 802.11g combo mode. This
will seamlessly switch between bands during channel