Beacontalk is a simple chat program that uses wireless beacon frames to transmit and receive data.

To use Beacontalk, your wireless card has to be in monitor mode. Using the madwifi drivers you can achieve this by entering the following command. 

$ ifconfig wlan0 down; iwconfig wlan0 mode monitor; ifconfig wlan0 up

Where wlan0 is your wireless device of course. 
To put your wireless card back to normal change 'iwconfig mode monitor' to 'iwconfig mode managed'. 

Make sure the wificards you are using are on the same frequency. Using iwconfig you can set a frequency like this:
$ ifconfig wlan0 down; iwconfig wlan0 freq 2.412G; ifconfig wlan0 up;