Can i change TXPOWER of ORINOCO gold classic

Hi,
I am running an ad-hoc network on Mandriva(2006).It works fine. I am using Orinoco gold classic card by Lucent.
To do my experiment I have to change the transmit power of the card.Can anybody suggest where I can make the changes or any specific version of the driver that would allow me to do it.
When I try to change the TX power

#iwconfig eth0 txpower 6
I get an error: "Set Tx Power" (8B36)
Set failed on eth0:Operation not supported

Thanks in advance
Alex