You're asking the wrong question.
IPSec provides a secure, encrypted tunnel between two hosts. It does not mean that the hosts in question are secure in any way other than the traffic that passes between them.
At the very least, to stop people listening in on your traffic you would have to setup IPSec between you and your router, but that does not prevent other people using your AirPort base station to either attempt to compromise your machine or piggy-back on your ISP connection.
What is it you're trying to achieve?
If it's securing your that you're after, install (and properly configure) a firewall to block unwanted traffic. If it's preventing other people from snooping your traffic, use ssh tunnels to encrypt all traffic.
If you insist on using AirPort and you're paranoid, change your WEP key frequently.
IPSec provides a secure, encrypted tunnel between two hosts. It does not mean that the hosts in question are secure in any way other than the traffic that passes between them.
At the very least, to stop people listening in on your traffic you would have to setup IPSec between you and your router, but that does not prevent other people using your AirPort base station to either attempt to compromise your machine or piggy-back on your ISP connection.
What is it you're trying to achieve?
If it's securing your that you're after, install (and properly configure) a firewall to block unwanted traffic. If it's preventing other people from snooping your traffic, use ssh tunnels to encrypt all traffic.
If you insist on using AirPort and you're paranoid, change your WEP key frequently.