Wireless networking and ethernet switches.

Sounds like an airport express, just plug it into a wall and set it up using ur mac to avoid installing any software on other pcs in the house if you have any. select bridge mode and find your network. again this is done wireless, in WDS or bridge mode, so just plug into a wall and set it up. no wires, not even a power cord, as there already is a ac plug,

 

Airport Express seems like the answer to me, too. I need to get one for my kitchen, where my PowerBook G4 is kept. Right now, my network connectivity there ranges from slim to none but I believe an Airport Express, set to Extend a Wireless Network would do the trick.

 

2 choices, extend your existing wifi network using another access point wirelessly, or wired.

Wired is going to give you the most wifi bandwidth, wireless is going to cut in half the wireless bandwidth between the 2 wifi access points. 54mbits is now 27mbits.

If you can, run a wire to the other wifi access point.

If your wanting to do some work, find a wrt54g router you can install dd-wrt. Get 2 of them (~$60 each, cheaper sometimes on Ebay with dd-wrt installed already) and use WDS in them, crank up the amp to extend their range further and if you want to really extend the range, get some better than stock antennas.

I am not sure the size of your house, but my Belkin on one side of my house would give me spotty connections on the other side of my house. My DD-WRT hung in the same location, gives me spottLESS connections on the other side of my house, and even to that sides next door neighbors front yard. It gets spotty when I am in their driveway though. All I did was increase the amp's output. Off hand I cannot remember how high I went, but it was much higher than stock on those units.

Those TrendNets are crap in my opinion. An ISP I worked for sold them for a few months to our broadband customers. We spent more money shipping them back for RMA's than we made in profit selling them.

Edit: I say TrendNet in general, I have never heard of the specific model you refer to.

 

Good luck with using a non-apple device as the main base station, sometimes apparenlty it doesn't "just work" (something to do with the way passwords are handled). might be an easier setup to purchase a second airport and plug it in directly to your existing router, and use that for your wireless.
There is a post Here that i found, you may have to drop your network to WEP (easily crackable) to get it to work.
Or go with a non-apple unit.

also you will take a speed hit when relayed as opposed to a straight connection to a wireless base station.

If you can get an Ethernet cable to a central location and plug the express into that it would be your best bet. if the network is setup properly, your devices will "roam" from one base to the other seamlessly.