Windows XP and Office 2003 files in a Microsoft Network

I have a Microsoft Network with 4 Computers (one has
Millenium, ones has Wind 98 and one has Win 95 and the
one with a problem with Windows XP)

It is working all OK but only one problem. If I try to
open a file of Office (word or excel or power point, any
version) that is sitting in the hard disk of one of the
computers, and I try to open with the computer with the
Win XP version, it just does not open it. However, if I
try to open a photo from the XP computer of a file
sitting on another computer it works.

Samewise, if I create a file with word or excel on the XP
compuyter and I t4ry to save it on the other computers,
it does not allow me either.

Is there any conflict with Office 2003 on that newtwork?
How can I fix it?

DMB