what you want to use is called ICS Internet connection sharing. plug the cat5 into your laptop then to your desktop. go to your wireless network adapter (XP is under network properties or vista/7 is under network and sharing center and adapter properties). double click on it and go into properties, from there go to advanced and check the box that says share this connection. hit apply and your lan card will change your ip address and your done. if you need to port forward you can go back into this same option and click settings, in there you can add any number of ports for udp or tcp traffic.