Looking around the sites it seems that I am one of many who have failed to get ndiswrapper working with OpenSuse 11.1, but while some workarounds have been found for some drivers, mine isn't among them.

I am using using a SpeedTouch ST121G USB adapter. This worked in Suse 11.0, but not 11.1. It uses a BT4501G driver; not one of the common ones, it would appear. Suse 11.1 does not see the interface at all, although I have made all the appropriate entries into the appropriate ifcfg file. Using Yast and entering 'ndiswrapper' into the Module field when I try to configure the adapter simply leads to its disappearing when I go back in to look for it. Presumable its disappearance is linked to the failure to pick up the interface when I use kwifimanager.

Anyone got any ideas/advice/success where I have failed?

perhaps you want to check that ndiswrapper is installed correctly? I know there are some troubleshooting methods when ndiswrapper is installed that you can use to check if the driver is loaded. something like... (forgive me if I'm lecturing to an ndiswrapper veteran)

ndiswrapper -l
checks the status of your driver. If it's correct you should see something like:
YxYxYx: driver installed
Device (XyXyXy) present

depmod -a
modprobe ndiswrapper

if there's no error with the first command, do the second. It loads the module, which will allow the ndiswrapper to finally work.

if there's actually no error there, then I would bet it's yast (if you're using yast) that's failing. Usually if I put in a card it stays there. For instance, I just added a wireless card with ndiswrapper, and it's still there when I go back. (I don't even have ndiswrapper installed on this computer).

Another check is to make sure ndiswrapper has the right driver and if it shows anything else it will have to be blacklisted before your current driver will work.