Please bear with me - I'm one of those annoying people who knows "a bit" about computers.

I've got this weird problem where my Ubuntu installation can't access my own wireless router when run from a specific laptop.

The problem appeared a couple of weeks ago on a WUBI installation of 10.04 on my laptop HDD. One day it worked, the next day it didn't. Ubuntu was updated and the laptop was rebooted into Win7 between it working and not working. I didn't think much of it, because I only really used Ubuntu for syncing my old phone. I actually deleted that installation, but I've started again with a different setup, and the problem is still there.

I now have Ubuntu 11.10 on SD card. I have a router we'll call "Netgear", my laptop we'll call "Medion" and my wife's laptop we'll call "Dell"

If I boot Ubuntu on the Medion, I can use Netgear through ethernet only. Wireless keeps asking for a password.
If I boot Win7 on Medion, I can use Netgear wirelessly.
If I put the SD card in and boot Ubuntu on the Dell, I can use Netgear wireless.
All of the above has been tried with the Netgear settings that used to work, and with Netgear set to factory defaults and no wireless security.

Using Ubuntu on Medion, I can access a neighbour's unsecured wireless router (also, coincidentally, called NETGEAR)
I can set up a secured wifi hotspot on my Android phone, and Medion can access that wirelessly.

I've no idea what to try next...

seems to me that ubuntu 11.10 don't have wireless drivers for your card anymore. Try linuxmint or crunchbang instead that come with wireless drivers preinstalled.

4 ways to get wifi working on linux

But wireless networking works on Ubuntu 11.10 on my laptop.

I can connect to other wireless networks, just not the one I need. It's been said on the netgear page that the chipset in my laptop and the chipset in the router are incompatible.

But if that were the case, I wouldn't have been able to connect weeks ago.

maybe you can disable encription and try again..that alone can solve the problem

Managed to get it to work. When all the alternatives had been exhausted, it was fairly certain that it was something that died in a 10.04 update that has been perpetuated to the 11.10. As it turns out - it was the Ralink 2800 "generic" driver which no longer worked. Updating to the 2860 as per the instructions here and it worked.