What Wifi extender would be compatible with my older Airport Express?

Apple designs their products to work with other Apple products, so if you are asking about extending using a wireless connection, you will almost certainly need another Apple AirPort router to accomplish the task. In other words, if your AirPort is capable of being extended, it would be extremely unlikely that a device from another manufacturer would be compatible to extend the signal.

Since there are four different versions of the AirPort Express, it is not really possible to know what device that you have now.....to be able to tell you whether it is capable of being extended or not with another Apple AirPort.

Locate the model number on the side of the Express. It is hard to see with gray lettering on a white background, so you may need a magnifying glass and good lighting to see the model number.

If you have model A1264 or A1392......then another A1264 or A1392 will be able to wirelessly extend the AirPort that you have now.

If you have model A1084 or A1088.....these are older models that do not have an "extend a wireless network" feature, so you will need to purchase at least two new devices to extend the network.

Sorry, I notice that you said I would need TWO more devices. What a drag..

Yes, you need two of either the A1264 or A1392 versions.....or another Apple router like the AirPort Extreme or Time Capsule...... if you want to extend the network wirelessly.

The A1084 is at least 9 years old. It should have failed about 4 years ago, so you are way ahead of the curve. Pat yourself on the back for your good luck.

Someone is selling two A1084's on Craigslist but if these are on their last legs, I will certainly NOT buy.

We've already mentioned above that these models do NOT have a setting to "extend a wireless network", so they will NOT do what you want. You need to erase your thoughts about the A1084 or A1088 version of the Express if you want to "extend". It cannot do it.

One more question: Airport Extremes are also available second-hand. If I buy ONE of these, will that do the trick?

You would need two AirPort Extremes to do what you want. The flat, square version......NOT the round or dome version.

The least expensive way to do what you want is locate two AirPort Express Model A1264 devices. I'm not really recommending that you do this, since the AirPorts will be at least 3 year old and probably closer to 6.

Your best bet would be to use two A1392 versions of the AirPort Express. That way, you know the product is not more than a few years old.

Apple sells refurbished AirPort Express A1392s on their online store for $65 each, with NEW warranty. New, the products cost $100 each, so you save $70 buying two. More info here, if you are interested:

http://store.apple.com/us/browse/home/specialdeals/mac/mac_accessories

When they arrive, do I need to UNinstall my old one?

No

But for the second installation, do I need land cable in order for it to work?

You will have optimum performance if both AirPorts connect with each other using a permanent wired Ethernet cable connection.

But, the second AirPort can extend the signal from the first using only wireless....IF.....the second AirPort is located where it can receive a strong wireless signal from the first.

Tell us whether or not you can set up a permanent Ethernet cable connection between the AirPorts......highly recommended.....or whether you want to try to extend the network with the second AirPort Express using wireless.....and not Ethernet.