I sounds like you have all the required hardware to make it happen.
Wireless networks are based on a ew common settings. All of which should be configurable through a web browser. Your ISP should at the very least provide you with basic setup instructions.
1. SSID or network name, and whether or not to broadcast that information. I would suggest not broadcasting the SSID for security sake. This means it will need to be entered manually (case sensative) on all clients computers that wish to join the network. If you don't know the name, you can't join.
2. Since the dawn of wireless there have been many types of communication technology, but since you're on a mac I'll tell you that 802.11b(Airport 11mbs) and 802.11g(Airport Extreme 54mbs) are the only two Apple supports. Your router way support more but "Wireless G" is what you have.
3. Security. There are many ways to secure your wireless network. WEP and WPA are two common and supported encryption methods for Airport Extreme and most UPnP wireless routers. MAC address filtering or hardware address filtering is another way to secure your network. I suggest using WPA and MAC address filtering. MAC address filtering will only allow computers that you have told the router exist and are allowed to join the network, and WPA will encrypt the communication of the wireless network.
SO,...Don't broadcast you SSID, encrypt your network with WPA and restrict computer access by MAC address filtering.
If you are having communication issues break it down to no security and add one component at a time to see where the trouble lies.
Good luck.