Vista - USB Wireless Adaptor Install Problem

Hi,

I've a new Dell inspiron 530s running Vista. I managed to install my old
Sagem Fast 800 modem router via USB. I made mistake of downloading drivers
from SAGEM site and it never worked again. Had error: -

"Windows found driver software for your device but encountered an error
while attempting to install it. The System cannot find the file specified."

I've bought a netgear dg834n which works OK via network port but I've just
tried to install a wireless wn121t usb 2.0 adaptor and get same problem.
System Ids new hardware as MARVELL Wireless Device. What file cant it find?
Has SAGEM driver update corrupted something? There appears to be a windows
update for this device but I cannot get it to load either.
--
Winker