Q: How do I extend my wifi using Airport express with my time capsul?

Read my post in the thread I've linked to below. It shows screenshots of the settings for the Time Capsule to 'Create the network' and settings on the Express to 'Extend the network.'

https://discussions.apple.com/thread/3703370

Yes, you can extend the signal using the newer version of Airport Express (AX) that has the "n" wi-fi...

That's all Apple sells but in case you are going to buy a used Airport Express, make sure it is the "n" version.

See this Apple doc:

http://support.apple.com/kb/HT4259

If you are using Lion OS X (minimum 10.7.3) you will want to use Airport Utility 6.0 in the Utlity Folder. If you are using Snow Lepoard, you will want to use Airport Utility 5.6 in the Utlity Folder.

You will not need more than one modem.

Message was edited by: Carlo TD

If you are using Snow Lepoard, you will want to use Airport Utility 5.6 in the Utlity Folder.

AirPort Utility 5.6 for Mac OS X Lion  will run on Lion, but not on Snow Leopard.

If you have Snow Leopard, you will need to use AirPort Utility 5.5.3 for Mac

I was pretty sure I had 5.6 before I upgraded to 6.0. and after upgrading to 6.0 It gave me the option to redownload 5.6 because one of my airport express was an older one. Mia culpa. Thank you.

Message was edited by: Carlo TD

You need to pay attention to something, while extending your network with the latest AirPort Express upgrade, your devices will be connected to it except your iPhone, you'll see your iPhone always connected to the capsule instead, even if you're at 1 foot from the AirPort Express.

You need to change the radio settings from automatic to 802.11a - 802.11b/g on your capsule, then I put it back to the default settings...

Now in the AirPort utility you should see your iPhone connected to the AirPort