The Mini can't be updated any more and is being used as a hard drive. If I put it where the wireless signal falls off, the rear of a clothing store with tons of metal racks where the last 10 feet of the showroom can't pick up the network, will that help?

Quite likely, yes. Better yet, run an Ethernet cable to it, and then set it up to do sharing of the Internet connection from the Ethernet cable.

Tacit's right: sharing the Internet connection via ethernet from the Mini is what will work here, whether the Mini itself gets its connection via WiFi or ethernet. Unfortunately, you cannot use the Mini to extend your WiFi network and make it a wireless repeater as you say in the thread title, because Airport Utility won't see the Mini as an option. If you need WiFi throughout the entire store, use an Airport Express to extend your existing WiFi network, and place it in range of the existing network towards the rear of the store.

We have a repeater. There is still a dead zone.

I have two repeaters, Airport Express, because of dead zones and I still find places where I have to switch between the 2.4 and 5 GHz bands to get optimum signal strength.

Please explain. They are using an Apple repeater, not the Airport Express, tho. I thought the wireless router (a Cisco)automatically switches from 2.4 to 5 as needed?

Your repeater options from Apple are limited to the Airport Express or the Airport Extreme. With few exceptions, neither can extend a non-Apple WiFi network.

I've been able to get WDS working with non apple wifi? You just can't use the setup wizard?

WDS based equipment is indeed the exception I was referring to, but I chose not to use it myself nor expand upon it here mainly because of your own comments about it elsewhere in these forums:

Is WDS the same as Access Point wall socket plug-ins?

No. WDS is the WiFi repeater protocol used by Apple and a few other manufacturers. Unfortunately, however, there are few non-Apple WDS-compatible routers or repeaters, and the level of compatibility is debatable, which may cause problems.

In contrast, Access Point is essentially ethernet over power lines, although the AP adapter itself can provide either WiFi or (wired) ethernet network access.

So the Access Points have to be on the same electrical circuit, not just the same location?

I have a similar question: I just bought these RCA plug in devices that I can connect to the phone jack and outlet, and then continue to put ones in power plugs and attach phones to them. Are they wireless transmitters or does the phone run over the power line?

- No, the APs can be on any circuit within the same service unit (home/business).

- In contrast to power line networking hardware, I believe that the RCA phone jack extension devices you're referring to use a high frequency radio band to communicate between units. That's wireless (like indoor wireless phones), but not WiFi.