I want to say that WIn98 uses something that Win7 doesn't. NetBIOS maybe? I can't remember exactly what.
BINGO! Thank you!!! That did the trick, W98 and Vista machines can now see each other.
I had tried enabling NetBIOS for IPv4 on the Vista laptop previously, but other settings have probably changed since then (I'll have to try remembering what).
I now have bidirectional access to files between my W98 laptop and my Vista laptop. I have unidirectional access between my W98 desktop and my Vista laptop (can access the W98 files from Vista, I'll need to investigate why it's not reciprocal as with the W98 laptop). Of course, I also have bidirectional access between the W98 desktop and W98 laptop (that's nothing new).
PS#1. Correction : Further testing reveals that bidirectional communications between either W98 machine and the Vista laptop is problematic. Accessing anything from the Vista laptop on the W98 machines is unbelievably slow and sometimes results in an error, no doubt due to some internal timeouts. Accessing data from the W98 machines on the Vista laptop works normally.
PS#2. One of the changes made to the Vista configuration was in registry key HKLM\SYSTEM\CurrentControlSet\Control\Lsa :
Other values I may have changed in the same registry key :
Edited by jds, 20 May 2012 - 12:58 AM.