Hi Paul I came across this site as I was searching how to make my new WG111v3 usb adaptor work under mandriva 2008 (I'll try it on my ubuntu machine later) - that has ndiswrapper installed and, like yours, didn't work. Your posting gave me the clue as to where to look (as well as reading the ndiswrapper manpage), so if you, or anyone else is still having problems, this is how it is done.
The wg111v3 comes with a setup.exe file, rather than the raw inf and other files, so the trick is to extract the files that you need from it. I have wine installed so I simply ran it under wine and went back to harvest the necessary files - you might also use an extraction tool such as filejuicer to get at them, or even use setup on a windows machine!
You need WG111v3.inf which is in .wine/c/windows/inf/ wg111v3.sys which is in .wine/c/windows/system32 I also included wg111v3.cat which is in .wine/c/windows/inf/WG111v3/Vista64 but I don't know if you actually need it
the .wine file is usually in your home folder, c may also be called drive_c or fake_windows
Copy these files to a folder somewhere and use them to configure the ndiswrapper. The mandriva wireless configuration tool in the control centre worked fine after that (when I remembered to actually plug in the adaptor) and automatically installed the extra files needed for wpa encryption; I am sure the ubuntu tools will work equally well.