"using compression? ya thats a very good possiblity. Your xbox then would have to stream an already compressed movie, thats compressed again. Since all 3 of your boxes are having the same probably goes back to the server."
NO!
That is not how compression over shares works at all.
As Windows retrieves the data from the drive a fairly low level process. The data is passed to the server software already uncompressed.
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To the original poster;
Things you might want to check.
Is Windows set to permit the Lan Interface to power down to save power?
Likewise do you have any power savings or drive spindowns?
Windows will not see any activity from the user and may be invoking power saving modes.
Your hub router may see high collisions (is your data travelling thru a data rate change, say from 100mbps to 10mbps thru a slower link or hub). This will cause the more intelligent devices to believe that you have a chattering device on your network and shut down it's link temporarily.
Do you have mutiple paths to the same devices ANYWHERE on your network?
E.G. dual homed machines, or hubs/routers interconnected via more than one cable or in a round robin fashion?
I've used Samba streaming since it's initial support off WinXp, WIn2k & Win2k3 server w/o any similiar problems EXCEPT when one or move of the above occurred.