We have a program that enables those other computers to connect to one of the computers (called RR on the network) that runs a server-type program. One computer has been wiped clean and I'm now trying to re-install the client (I think that's what it's called) program to connect to the server program on RR.
I know through the "ODBC Data Source Administrator" I have to connect the client computer to the server one (RR).

In that ODBC panel I have copied what is on the other already connected computers: I click "Add", then fill in the same "Name", "Description" and "Server". The server field is : RR\SQLEXPRESS.

I then click next and set the same settings as the other connected clients: "With Windows NT authentication...", and "Connect to SQL Server to obtain default settings..."

Then when I click "Next" it obviously tries to connect to RR\SQLEXPRESS, but can't and comes up with the error:

The client computer has MS SQL Server compact 3.5 and 4 installed. Also .NET 2, 3 and 3.5. The computers are connected fine over the network.
Is anyone able to please assist this not-really-that-geeky person?