I just installed a new 802.11 b/g AP to replace a b-only unit.  
However, when I configure it for g-only mode, my laptop (Thinkpad T42 
with a/b/g Atheros card) it wasn't talking.  Do I need to do anything 
special?  (The access point is about a meter from the laptop.  Another 
(NetBSD) laptop further away couldn't talk, either, when I set the AP to 
g-only.)

$ dmesg|grep ath
ath0 at pci2 dev 2 function 0
ath0: interrupting at irq 11
ath0: mac 5.6 phy 4.1 5ghz radio 1.7 2ghz radio 2.3
ath0: 11a rates: 6Mbps 9Mbps 12Mbps 18Mbps 24Mbps 36Mbps 48Mbps 54Mbps
ath0: 11b rates: 1Mbps 2Mbps 5.5Mbps 11Mbps
ath0: 11g rates: 1Mbps 2Mbps 5.5Mbps 11Mbps 6Mbps 9Mbps 12Mbps 18Mbps 24Mbps 36Mbps 48Mbps 54Mbps

b133$ ifconfig ath0
ath0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
        ssid machshav nwkey *****
        powersave off
        bssid 00:0f:66:77:73:d3 chan 3
        address: 00:05:4e:4d:3e:20
        media: IEEE802.11 autoselect (OFDM54)
        status: active
        inet 192.168.2.6 netmask 0xffffff00 broadcast 255.255.255.255
        inet6 fe80::205:4eff:fe4d:3e20%ath0 prefixlen 64 scopeid 0x2
b134$ wlanctl ath0
ath0: mac 00:0f:66:77:73:d3 bss 00:0f:66:77:73:d3
        node flags 0001<bss>
        ess <machshav>
        chan 3 freq 2422MHz flags 00e0<cck,ofdm,2.4GHz>
        capabilities 0011<ess,privacy>
        beacon-interval 100 TU tsft 94672261 us
        rates *1.0 *2.0 *5.5 6.0 9.0 *11.0 12.0 18.0 24.0 36.0 48.0 [54.0]
        assoc-id 49155 assoc-failed 0 inactivity 0s
        rssi 63 txseq 1856 rxseq 2193
ath0: mac 00:0f:66:75:3d:75 bss 00:0f:66:75:3d:75
        node flags 0000
        ess <machshav>
        chan 8 freq 2447MHz flags 00e0<cck,ofdm,2.4GHz>
        capabilities 0411<ess,privacy,short slot-time>
        beacon-interval 100 TU tsft 18138390 us
        rates *1.0 *2.0 *5.5 6.0 9.0 *11.0 12.0 18.0 24.0 36.0 48.0 [54.0]
        assoc-id 0 assoc-failed 0 inactivity 0s
        rssi 13 txseq 0 rxseq 0
ath0: mac 00:0f:66:75:3d:75 bss 00:0f:66:75:3d:75
        node flags 0000
        ess <>
        chan 8 freq 2447MHz flags 00e0<cck,ofdm,2.4GHz>
        capabilities 0411<ess,privacy,short slot-time>
        beacon-interval 100 TU tsft 18329988 us
        rates *1.0 *2.0 *5.5 6.0 9.0 *11.0 12.0 18.0 24.0 36.0 48.0 [54.0]
        assoc-id 0 assoc-failed 0 inactivity 0s
        rssi 13 txseq 0 rxseq 0
ath0: mac 00:0f:66:77:73:d3 bss 00:0f:66:77:73:d3
        node flags 0000
        ess <machshav>
        chan 3 freq 2422MHz flags 00e0<cck,ofdm,2.4GHz>
        capabilities 0011<ess,privacy>
        beacon-interval 100 TU tsft 94672261 us
        rates *1.0 *2.0 *5.5 6.0 9.0 *11.0 12.0 18.0 24.0 36.0 48.0 [54.0]
        assoc-id 0 assoc-failed 0 inactivity 0s
        rssi 54 txseq 0 rxseq 0
ath0: mac 00:0f:66:77:73:d3 bss 00:0f:66:77:73:d3
        node flags 0000
        ess <>
        chan 3 freq 2422MHz flags 00e0<cck,ofdm,2.4GHz>
        capabilities 0011<ess,privacy>
        beacon-interval 100 TU tsft 441446794 us
        rates *1.0 *2.0 *5.5 6.0 9.0 *11.0 12.0 18.0 24.0 36.0 48.0 [54.0]
        assoc-id 0 assoc-failed 0 inactivity 0s
        rssi 56 txseq 0 rxseq 2194


		--Prof. Steven M. Bellovin, http://www.cs.columbia.edu/~smb