Mapped drives everywhere

Suddenly 2 of my 10 xp workstations are mapping every available drive after
booting up
All the drive letters ( other than C and D and my one normally mapped drive
to the server) ) appear with "disconnected network drive" beside them, if I
double click I see the contents of my "normally" mapped share, And I cannot
disconnect the drives as they are already showing as disconnected. If I
reboot my system my normal drives and one share appear, then about a minute
later all the other drives appear again.... Any Ideas? I have scanned for
viruses etc.

Thanks