Time Capsule setup

Your old Time Capsule can certainly be used wirelessly to "join" the network. That being said, you will experience lower performance during data transmission to and from the older Time Capsule as it must go wirelessly. Ethernet is always the best bet, but I understand your reasoning.

To begin, locate the reset button on the rear of the old Time Capsule. Remove the power cable and depress the reset button. Plug in the power cord while still holding reset until the front light begins to blink rapidly. You may now release the reset button. The Time Capsule has now been reset to factory settings, and is pending setup. Please note that this does not wipe the data off of the hard drive.

Begin by opening AirPort Utility. The latest at time of writing is 6.3.1. You should not need 5.6 unless that you need more advanced features, or you have a really old Time Capsule. Inside the window you will see three things. A globe labeled "Internet" with a solid line running into the first Time Capsule. Locate the "WiFi" settings up in your menu bar. Within that drop down you will see the Time Capsule as an "Other AirPort Device or Base Station", select it. AirPort Utility will begin to look about the network and commence the setup process.

By default, AirPort Utility may suggest to extend the network (wirelessly). You will see "Other Options" in the bottom left of the window. Select that! Then choose "Join a Network", select your network, and enter the password for the wireless. It may ask you a few more questions like the base station password of the other Time Capsule as well. Continue through the setup process.

Once complete, wait a moment for the Time Capsule to initialize the settings and negotiate itself as a member of the network. You should now see "Internet" with a solid line to the first Time Capsule, with a dotted line to the second. The dotted line means that the transmission is wireless.

If my quotations are slightly off it is because I wrote this out of memory. Don't worry though, it is always easy to reset them if something goes wrong...