samba - Dec 2007 - shares mount but not visible under My Computer in XP

Greetings,
Have winXP computers and laptops logging onto debian server now running
samba 3.0.24.  Recently I have noticed some users cannot see all their
allocated shares under My Computer.  New laptops added to the domain only
receive H: [their home] and z: [their profile] shares.  If I try to map a
drive eg N: [network] a prompt informs me that is already mapped.  I can
also view the contents of the share via the run menu and \\server\network.
The problem is the shares no longer appear under My Computer.  I thought the
problem was cured when I noticed some of the share names in the logon bat
files were in lower case letters and when changed to capitals appeared to
enable users to mount all their shares under My Computer.  However with a
new laptop just added to the domain they still only receive home and profile
shares under My Computer.
Any ideas as to what I have done wrong?
Regards