All comps cannot access server

Hello,
we have a Local area network setup. the problem is that some of the comps cannot connect to the server though net is working on them but they cannot access files. similarly on other comps only one or two comps are visible but not the whole network.
solution desired:
if anything can be done so that all comps can see full network in their network places and access the shared files and folder please do advise.
we want to share folders on server so that material in these folders is available to everyone and all can access it , copy stuff from there and put stuff there.
network:
its a small office network with 10 computers running on windows XP.
please advice.
thnx