"168.0.1. is not a valid IP address."
Don't worry, I was just using shorthand.

Pinging 192.168.0.1 and 192.168.0.2 gives me the same message;
"Network is unreachable."....which I think we already guessed??

You said the router is either not hearing, or not listening for the DHCP request.
Is this an error by Linux, or could NDISWrapper be the cause? I've uninstalled and
re-installed NDIS and the USB's driver, and done "modprobe" so the PC can see
both and use them. Is there a setting that will make NDIS issue the DHCP command, or
do I need to change something elsewhere to make sure it's sent?

In future, please don't use "shorthand". I do not think you would like it if I gave you "shorthand" commands to test things out

Is, I think, where you should start looking.
Parts of your wireless connection are working ( eg iwlist scan shows that your WAP is broadcasting and your PC sees it, so your wireless driver is probably working).
But no connection is established

Means just that: something basic and essential to networking is not working.
I am very puzzled as to just why the installation, and then removal of guarddog / firestarter could cause this.

Did you, perhaps, change anything else, whilst you were trying to get guarddog / firestarter to work? Please think back.

As usual, searching the web for error messages helps. I just searched for Error for wireless request "Set Encode". There are quite a lot of links.

I suggest you try the same, and see if any of the advice offered is applicable to your situation.

Good news, Tredegar - It works! I have no memory of doing anything other than
installing and trashing Guard Dog, but it caused three days of sheer hell. All
I had to do was turn off the WEP and the PC connected - first time! Now Linux
is back and the world makes sense again. Thanks for all your help!

Be well, be happy,

Michael