Read over Ethernet - Arduino Reference.
Your Airport IP is most likely your gateway, DHCP & DNS IP. In your code, destIp should be your computer's builtin ethernet IP, myIp should be an IP address that is not in use by any other device on your network. I have no idea what your network looks like so I can't say what IP will be unused. Try using the ping command in terminal to see if you get any replies before using a random IP for myIp.
On most home networks, your subnet is 255.255.255.0. That means all the devices on your network will share the same first 3 octets, only the last octet in the IP address will change. For example, if the router/gateway IP address is 192.168.0.1, then your computer IP should be 192.168.0.x, and your Arduino's IP should be 192.168.0.x (different than the computer, where 'x' means a number from 2 - 254, 255 is reserved for broadcast msgs). I can't guarantee that your network is like I just described. Run ifconfig, you probably have a connection named eth0, note what it's inet addr and mask are. That is your computer's IP address and your network's subnet mask. Usually, all devices on the same network have the same subnet mask.
If the IP addresses in your code are the actually addresses you are trying to use, you will have problems. destIp looks like a randomly selected IP due to a lack of a DHCP server, usually also with a 255.255.0.0 subnet. With those IPs, your arduino and computer will not be able to communicate.