I've got exactly the same problem - the realtek driver loads, lights on the card blink wildly (usually), but it fails to communicate with the base station. Unloading the driver hangs the system. Setting the channel using iwpriv wlan0 wlan_para channel=x does nothing, the channel always shows as "0". Using a tcpdump on the device shows that it is not getting a response when it sends arp requests.

Any ideas? What cards actually work with (Debian 3.0) Linux?