My grateful thanks to "texasred218" for your reply. Following your suggestion I tried a "live" version of Ubuntu 10.04 alpha from Linux Mag. but it did not recognise my Ralink wireless adaptor, however, in the Ubuntu forums under:-
"Ralink RT3090 Wireless Not Supported in Lucid"
I found this solution which worked like a dream:-
I would just like to confirm that the workaround suggested by Carsten seems to work perfectly (so far).
mkdir -p /etc/Wireless/RT2860STA/
service network-manager restart
It is then possible to connect via network manager.