Can I connect a wireless printer to two wireless networks

Question

I searched and couldn't find an answer to this exact situation. The answers to similar questions didn't seem to work.
Can we share a wireless printer over two wireless networks without adding hardware or changing the wiring or doing complicated software modifications?
Here is my set-up:
Cable Modem> Linksys Wireless Router “N” on the first floor > older AirPort Extreme “G” via ethernet cable on second floor > Laser Printer via USB Cable on the second floor, plus an AirPort Express to extend the area on the second floor. We have 2 MacBooks and 1 MacBookPro that connect to the internet via either of 2 wireless networks. Generally, for better connection, you choose “N” if you are on the first floor and “G” for the second floor.
Currently, if you want to print to the USB Printer, you just select it in the print dialog box. It does not matter if you are on Network “N” or Network “G.”
We just added a new wireless Printer that’s on the first floor. (No, I didn't read the directions, the printer screen said if there is a W?? button on your router, press it. I did and it automatically connected to the “N” network. It also has its own email address for printing without a computer, but that still doesn't solve this question.)
If you want to print to this printer, you must first change the computer’s AirPort setting to join the “N” network. If you don't, you still get the print dialog box, but eventually you will notice that nothing happens. The document just sits in the Printer’s queue.
Is there a way to get a computer on the “G” network to find the wireless printer on the “N” network without first changing networks?
Remember, it automatically finds the USB printer that is plugged into the “G” network router.

Answer 1

It used to be that if you wanted to wirelessly extend the range of a network, you'd have to set up a WDS. (WDS = Wireless Distribution System.) There was no "Extend a wireless network" option and no "Allow this network to be extended" checkbox—you'd have to fill out lots of WDS information yourself. It was sort of a pain.
Then, with the 802.11n AirPorts, Apple introduced the "Extend a wireless network" option, greatly simplifying the setup process. It accomplishes the same thing as a WDS, but it's easier to set up and has less overhead. However, it can only be used if every AirPort in the wireless network supports 802.11n.
Your Express may support 802.11n, but your Extreme is older and does not. So "Extend a wireless network" won't work for your network. That's why you got errors when you set the Express's "Wireless Mode" option to "Extend a wireless network." Instead, you'll have to do things the old-fashioned way* and configure the Extreme and the Express to be part of a WDS. Your network will still work as desired: the Express will rebroadcast the signal from the Extreme, and clients will connect to whichever station has the stronger signal. It's just that you'll be using the older WDS technology instead of the newer "Extend a wireless network" feature.
"Join a wireless network" is something different entirely. You'd use it if you wanted to connect to a network but not rebroadcast it. This could be useful when, for instance, your main router isn't an AirPort but you want to use AirTunes. In your case, however, this option wouldn't be very useful.
Look at [this thread|http://discussions.apple.com/thread.jspa?threadID=2588489] for more information.
*Actually, the old-fashioned way would be to use modems. Or to forget about the internet and send snail mail instead.