My PC runs on Windows XP sp3. It has an integrated LAN card which I use to connect to internet and a wireless card which I'd like to use to share the internet at home via an ad-hoc network.

Windows XP doesn't offer WPA encyptions for ad-hoc networks and WEP is seriously flawed. I have no interest in buying a wireless router since I am going to share the connection only on special occasions.

I was thinking about improving security by denying any access from machines that have a different MAC or IP address than the approved ones. Would this be possible with the free ZoneAlarm and how effective would that be?