How to create a Trusted file location?

1.    From Administrative Tools, open the SharePoint Central Administration Web application.
2.    On the Central Administration home page, click Application Management.
3.    On the Application Management page, in the Office SharePoint Server 2007 Shared Services section, click Create or Configure this Farm's Shared Services.
4.    On the Manage this Farm's Shared Services page, click SharedServices1 (Default). This is the Shared Services Provider (SSP) that you will configure.
5.    On the Shared Services home page, in the Excel Services Settings section, click Trusted file locations.
6.    On the Excel Services Trusted File Locations page, click Add Trusted File Location.
7.    In the Address section, type the location and name of the SharePoint Office SharePoint Server 2007 document library that you want to add as a trusted file location in Excel Services. If the document library is stored in the Windows SharePoint Services 3.0 content database, ensure that Windows SharePoint Services 3.0 is selected as the Location Type.
8.    In the External Data section, select the type of data connections that you will allow workbooks in this trusted file location to contain and click OK.
In the External Data section, you can determine whether workbooks stored in trusted file locations and opened in Excel Calculation Services sessions can access an external data source. You can designate whether Allow External Data is set to None, Trusted data connection libraries only, or Trusted data connection libraries and embedded.
If you select either Trusted data connection libraries only or Trusted data connection libraries and embedded, the workbooks stored in the trusted file locations are allowed to access external data sources. External data connections can be accessed only when they are embedded in or linked from a workbook. Excel Calculation Services checks the list of trusted file locations before opening a workbook. If you select None, Excel Calculation Services will block any attempt to access an external data source. If you manage data connections for a large number of workbook authors, you might want to select Trusted data connection libraries only.