Hi,
before running kismet, you should also run
# kismet_monitor
(to put your card into monitor mode; actually you may not need this, since, as you say, kismet runs OK, and I think that if this command was needed for you, kismet would die. Just try with and without :-)
# kismet_hopper &
(to have you wifi card jump between channels looking for APs)
# kismet
....
and, after finishing, remember to run
# kismet_unmonitor
(fo clearness)
Hope that helps.