iwconfig - SET failed on device

Hello,
Working with Intersil PrismGT mini-pci 11g driver. After loading the module,
check the wireless interface by iwconfig:

#iwconfig eth0

Warning: Driver for device eth0 has been compiled with version 13
of Wireless Extension, while this program is using version 15.
Some things may be broken...
Warning: Driver for device eth0 recommend version 15 of Wireless Extension,
but has been compiled with version 13, therefore some driver features
may not be available...
eth0 PRISM Duette ESSID:"uAP"
Mode:Master Frequency:2.437GHz Bit Rate:54Mb/s
RTS thr:off Fragment thr:off

Some warning message, but basically the card is able to work in AP mode.
Try changing the SSID:

# iwconfig eth0 essid myAP
# iwconfig eth0
Warning: Driver for device eth0 has been compiled with version 13
of Wireless Extension, while this program is using version 15.
Some things may be broken...
Warning: Driver for device eth0 recommend version 15 of Wireless Extension,
but has been compiled with version 13, therefore some driver features
may not be available...
eth0 PRISM Duette ESSID:"myAP"
Mode:Master Frequency:2.437GHz Bit Rate:54Mb/s
RTS thr:off Fragment thr:off

SSID able to change successfully. But when I try to change the bit rate,
encryption and txpower:

# iwconfig eth0 rate auto
Error for wireless request "Set Bit Rate" (8B20) :
SET failed on device eth0 ; Operation not supported.

# iwcofig enc 1234-5678
Error for wireless request "Set Encode" (8B2A) :
SET failed on device eth0 ; Operation not supported.

# iwconfig eth0 txpower 15mW
Warning: Driver for device eth0 has been compiled with version 13
of Wireless Extension, while this program is using version 15.
Some things may be broken...
Warning: Driver for device eth0 recommend version 15 of Wireless Extension,
but has been compiled with version 13, therefore some driver features
may not be available...
Error for wireless request "Set Tx Power" (8B26) :
SET failed on device eth0 ; Operation not supported.

Apparently the command is not working well. Any idea on this?