I have a Redhat EL5 server with one AR5416 PCI card (TP-Link 951N). I use the madwifi 0.9.4 to drive the card. It can run as a station well, but I want to run it as a wireless AP.

# modprove ath_pci autocreate=ap
# wlanconfig ath0 create wlandev wifi0 wlanmode ap
# iwconfig ath0 essid my5416 channel 2
# ifconfig ath0 up
# iwconfig ath0
ath0 IEEE 802.11g ESSID:"my5416"
Mode:Master Frequency:2.417 GHz Access Point: 00:25:86:20:EA:90
Bit Rate:0 kb/s Tx-Power:17 dBm Sensitivity=1/1
Retryff RTS thrff Fragment thrff
Encryption keyff
Power Managementff
Link Quality=0/70 Signal level=-96 dBm Noise level=-96 dBm
Rx invalid nwid:5 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:0 Missed beacon:0

I can find 'my5416' SSID in another PC and every thing is good. But When I try to connect it, it fails.

I tried hostapd, but failed also.

# ./hostapd -dd hostapd.conf
Configuration file: hostapd.conf
ctrl_interface_group=0
ioctl(SIOCGIFINDEX): No such device
hostap driver initialization failed.
ath0: Unable to setup interface.
rmdir[ctrl_interface]: No such file or directory
ELOOP: remaining socket: sock=4 eloop_data=0x9a46950 user_data=(nil) handler=0x8074da0

Does this "PC" keep log where you can see what goes wrong?

It is a WinXP. I do not know how to see its log. But I will follow your suggestion to see what happened using a Linux client.