Trouble with file sharing

I have a local area network with three PCs on it. One of them is an XP and
the other two are Business Vista and a laptop with Premium Vista machines. I
have set up shares on each machine. The problem is that the other machines
cannot access the laptop with Premium Vista’s shares. The other two can
access each other's and the laptop can access theirs.

The Business Vista machine doesn't even show that the laptop is on the
network. The XP machine shows it is their but when you try to access it says
that access is denied. I've checked the security and I set it up the same
way for the laptop's shares as I did those on the Business Vista machine. I
have looked all around but have not found any how to documentation that would
tell me if I left out a step.

Can you help me solve this problem?

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Thank you,

Tom