I have a customer who has 15-20 computers in a workgroup & shares files
between them all.
They bought Norton Internet Security 2006 for all of them & the personal
firewall blocks them from sharing files between them.
What services/applications, etc., need to be changed so the firewall stays
on, but files can be shared?

The intelligent man wins his battles with pointed words.
I'm sorry -- I meant sticks. Pointed sticks.