Using a Netgear WG511T (5212 chipset) in a Dell Inspiron 7500 I can't set a channel/frequency with iwconfig. If the adapter is down (ifconfig ath0 down, ifconfig wifi0 down) I can set the value and subsequent iwconfig commands will show the frequency that I set. On bringing up the adapter, though (ifconfig ath0 up), it begins scanning through all channels and cannot/will not connect to my AP, which is broadcasting on a fixed channel. Issuing the iwconfig commands multiple times yields a different freq setting each time. The iwconfig ath0 freq 2.437G and channel 6 command have no noticeable effect when the card is up; the channels just keep scanning. I can connect on _rare_ occasions - I believe it's just luck of the draw with the card hitting the right channel at the exact instant the AP is broadcasting.
Info: Fedora Core 3; kernel 2.6.12-1.1381_FC3; madwifi-ng rev 1454(? svn'ed from trunk 2/22/06)