How to set up a secure computer to computer wireless network

There must surely be a simple manual suitable for a complete beginner (ideally a .pdf) that explains how to set up a secure wireless network between two Macs with built-in Airport Extreme, using the best level of security (which I understand is called WPA). But where would we find this manual? We read through LOADS of documents - most of which explain how to CONNECT to a ready-made network or how to set up a wireless internet connection.

All we want to do is to have a Mac Book Pro connect wirelessly AND SECURELY to an iMac G5; and for the G5 (which is hardwired to the Internet via a USB modem) to share its internet connection with the Mac Book Pro. We specifically want to ensure that neither our Internet connection NOR our computer-to-computer connection can be hacked into by anyone else!

This article might help you setup a secure wireless connection. If you are intending to use WPA which is the more secure method, try this.

Thanks for that. The first link was interesting but I got stuck at "enter your ICTP user name in the User Name box, and your ICTP user password in the Password box". As a relative beginner setting up networks I had no idea what this meant! I guesed that I was in the process of configuring the host machine so made up a user name & password expecting the other machine to need to enter the same info to connect. But from the error message (on the host) I got about not being able to connect I guess I was wrong! I didn't get as far as trying to set up the other machine. Are there any simpler instructions somewhere or can you perhaps help me past this bit? Thanks.