Short on time..
Windows doesn't really care about workgroup names if you connect using UNC path. It should just work.
Something is obviously misconfigured, most likely on the Windows 7 compyter.
Open network and sharing center :
Make sure you are on Home or Work network, NOT Public network.
In network and sharing center > advanced sharing settings
Make sure file and printer sharing is ON
Turn homegroup OFF
As a diagnostic turn on public folder sharing, then go to Vista and type in \\DELLDPN and see if the share then appears.
If you have shared a folder such as your "my pictures" then the NTFS ACL will stop the vista machine from accessing, unless you access from an identical account name with identical password on the Vista machine.
Still not working:
3rd party firewalls?
Check windows firewall that file and printer sharing is allowed.
Zen 8000 Active
Edited by Pipexer (Wed 18-Jan-12 23:20:35)