Well I’ve finally solved this issue.
Seems that I had 2 problems, both related to Edgy Eft
Firstly the distro apparently included a broken driver for my WG111v2 USB adaptor. Cure for this was to blacklist the dodgy driver and use ndiswrapper to package the Win98 drivers.
However, this flushed out the second problem – ndiswrapper is also broken in Edgy. It includes an incompatible version of the ndiswrapper-utils package.
Diagnosis was hampered by the fact that the WG111v2 worked for some things eg Firefox and Samba but not for multicast packets.
Anyway, its all good now, so thanks again for your assistance.