ok, I find AE works fine as a router....
Applications > utilities > Airport Admin Utility
Select your network, click "configure" enter password assigned when creating network, click "Show All Settings"
Check the box that says "Create a Closed Network" this makes it so that the AEBS does not broadcast its existence, you should set your computers to automatically join the correct network using the correct password, if you haven't assigned one, do that.
Click on "Base Station Options..." Uncheck the first 4 boxes if any are checked
If Wireless security is not enabled, click "Change Wireless Security..." In my experience, WPA personal is most secure, (except for enterprise, but you probably won't be able to set that up... and I couldn't help) but not all wireless cards support it. After that, 128 bit WEP and then 40. You will set a passord for logging onto the network here....
Now, click on the "Access Control" tab at the top. Click the "+" and then select "This Computer"
If you have any other computers on the network, you will need to add them manually... the MAC address can be found in System Preferences > Network > Airport > Airport ID
If you need to add PeeCees, I cna give instructions for that too, but I won't unless you ask....
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