This...

...is how I get myself into trouble:
Bought my dad a router/wi-fi, his being second-hand, old, and broken. Plus I couldn't persuade Hubert's tablet to connect wirelessly to it.
So I ordered one on-line from Staples and next day, when it arrived and I had read the box, I started to have second thoughts: his computer is old, a discarded Macbook of Enid's which I've made useful again by replacing the MacOS with Ubuntu Linux; maybe it wouldn't connect?
No problem, however: I'd just put the new one on our system and give him our (not very) old one, which I know works.
So I plugged it in. All the computers promptly hooked up to it.
But there was no security.
So I changed the wi-fi settings to provide security: no computers would log on.
I messed about with this for a while, but nothing worked. I looked on line, but no "fixes" worked, which was not unreasonable as none were trying to fix problems and symptoms that were identical to mine. Some of the suggestions for what one should do to connect a router to our Telus modem were downright scary, so I knew they would inevitably result in long conversations with disapproving Telus techies.  I didn't go there.
I put the old one back on, which made all three Apples happy, but confused the hell out of the Dell. I thought maybe if I upgraded its Ubuntu 12.04 to 12.10 this problem would just go away.
No such luck; the upgrade just created other problems (why did Python need to reboot? why wouldn't it? why was there no /tmp file space?)
Anyway, that's when I packed it in.
This morning, after following the dog and thinking for an hour, I decided to go back to Plan A. So I replaced our old router with the new one, taking care to unplug both the modem and my computer before doing so. I entered new wi-fi security settings. When I had finished, the Apples were happy.
Then I did a clean install of 32-bit Ubuntu 12.04 on the Dell, and now, after some tweaking, it's happy as well.
So is the Ubuntu partition on my iMac.
But the iPod Touch, which we use as our radio most of the time, wouldn't connect, not even when I entered the new security code. As a consequence it now logs, all by itself, into the Telus modem, and works again.
Good thing I'm retired.

This is slight revision of a letter I sent to Bruce, one of the few people I know who actually understands  this sort of thing... and possibly the only other person I know who is interested.