Creating a Data Connection between an Excel workbook and an Excel Data Source

Question

Hello,

I'm new to WSS and Excel Services and I'm having a hard time trying to solve this:
I'm trying to connect an excel workbook with an excel data source, but I can't see a way to create a Data Connection that uses an .xlsx file as a data source remotely.  I tried to use ODBC DSN but it seems to use files stored just locally or in my network.
I created a DCL and the libraries that hold the workbooks and the data sources.

Well, what I really want to do is to link one excel to another in the Sharepoint, so when one cell of these .xlsx files is changed, the other will be able to catch the value of this cell updated and use some formulas, is there a way to do that?

I appreciate any help you guys can give me. Thanks.