Given the internal machines on on the other side of some router and share one IP address, your solution of using the MS Remote Access is going to fail. I will not be offering a reason why or how to possibly fix, but will note that only one machine could be accessed if you forwarded the ports needed. I will not tell you the port numbers since you need to learn how to find these on your own.
What can work is TightVNC since you can assign each machine its own port number and port forward each to each machine. I am not offering any assistance for TightVNC either since it's very well documented and your questions would be answered in the documentation.
Bob
I am in a network of 4 computers that connects to internet by a hub. When I send Remote Assistance request to an outsider computer (either by email or by Messenger), the other computer that accepts my invitation receives this error message: (I translated it into English as much as I can - the terminology may be wrong)
"Remote Assistance connection did not succeed as the other computer's name is not resolved. Please try again."
Both computers use Win XP and the settings to allow remote assistance (in the System/Remote tab) was made in both of them.
I really would appreciate any help. Thank you...

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