accessing hard drives connected by airport remotely

>Do I set up an external ip address for my airport extreme or is there one for it already?

Depending on the service type (consumer or business grade), your ISP provides your 802.11n AirPort Extreme Base Station (AEBSn) with a Dynamic or a Static Public IP address. Most consumer-grade service get Dynamic addresses; with business-grade getting either.

>Do I need to setup a dns, domain name or somehow register this ip address via dyndns.org?

To access the AEBSn and their attached drives, you would need to know the Public IP address. Since a Dynamic address will change periodically, you would need to use a service, like DynDNS, as you suggested.

The other thing that would be required is to configure the router for port mapping/forwarding to send AFP (for Macs) or SMB (for Windows/Linux) requests from the remote clients in order to access the drives.

>Do I need to setup an appletalk protocol?

No, this protocol should not be necessary.

>Do I need to contact my ISP and make arrangements through them to have this work?

You could ask, but most likely they will tell you that configuring personal routers for remote access is outside of their service agreement for basic Internet service. If; however, you feel more comfortable to have assistance, you may want to consider a service like Geek Squad.

>Do I need to set up a Leopard server on a Mac mini for this to work...

No, neither would be required. This can be done with just the AEBSn.

>Setup an out of range DHCP reservation (10.0.1.201)

Actually with DHCP Reservation, the IP address should be within the DHCP range. The reservation feature makes sure that this IP is not provided to any other network client, i.e., it is reserved to one specific client by its MAC address.

Ok, so let's go over the basic steps to see if anything was missed.

1. Start the AirPort Utility > Select the AEBSn, and then, note the IP address shown.
2. Select Manual Setup.
3. Verify that Connection Sharing = Share a public IP address is selected on the Internet > Internet Connection tab.
4. Select Disks, and then, select File Sharing.
5. Verify that both the "Enable file sharing" and "Share disks over WAN" options are enabled.
6. Verify that Secure Shared Disks = With a disk password. (Recommended)
7. Verify that AirPort Disks Guest Access = Not allowed. (Recommended)
8. Select Advanced, and then, select the Port Mapping tab.
9. Click the plus sign to add a new port mapping.
10. For Service, select the "Personal File Sharing" option. (Note: This option would only allow Mac clients to access the AirPort Disks. If you want both Macs and PCs to connect, you would need to leave this field at its default value and enter the appropriate SMB ports to the mix of ports to be opened.)
11. In the Public UDP Port(s) and Public TCP Port(s) boxes, type in a 4-digit port number (e.g., 8888) that you choose. In the Private IP Address box, type the internal IP address of your AEBSn that you wrote down in step 1. In the Private UDP Port(s) and Private TCP Port(s) boxes, type 548. Click Continue.
12. In the Description box, type a descriptive name like "AirPort Disk File Sharing," and then, click Done.
13. Click on Update.

To connect to the shared AirPort Disk from a remote location using a Mac:

1. From the Finder > Go > Connect to Server.
2. Enter the DynDNS-provided Domain Name or Pubic (WAN-side) IP address of the AEBSn, followed by a colon and the Public port number that you choose in step 11 of the previous procedure. For example: afp://www.mydyndnsdomain.com:8888 or afp://123.456.789.123:8888
3. Click Connect.
4. You should be prompted for your user name and password. The user name can be anything you like; the password should be the Disk password for the AEBSn that you created in step 6 previously.
5. Click Connect.

Ok, the instructions that I had provided assumed that the AEBSn is the ONLY router in your network configuration. That is, it is directly connected to an Internet modem ... not another router.

If your U-verse device is actually a combination modem/router or gateway, then the following would be the instructions you would need to follow: Gigaom - How-To: Access Your Time Capsule Over the Internet Note: Although this articles refers to the Time Capsule, it is equally valid for the AirPort Extreme.

If your AEBS is directly connected to the internet as the gateway router, there's no need to do any port-forwarding for your USB connected disks. Just "enable file sharing" and "share disks over wan". Also, AEBS will not work with the free dyndns account for dynamic dns. You will need to follow:

How to use dynamic global hostname so that you can resolve a hostname to your dynamic IP, and;

How to share disks over wan on the settings to share your disks over the internet.