Sharing files Peer-to-Peer in Windows Vista does not work

I have set a new Vista server on a HP computer and i have two other HP
laptops that are also using Vista. Currently, if Laptop A opens a Word
Document from the server computer, Laptop B is unable to open till Laptop A
closes it. This is done vice-versa also. This is not only for Word Document,
but all other documents.

But if i use another Laptop which is in XP mode, i can open the same Word
Document simultaneously from the server. But this is not the case of the
laptops are using Vista. I can only open a document one at a time. Please
help....

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Vignash Naidu