You can open a cube in Excel, as soon as it has been built by clicking the "Open in Excel" Button from the main screen, this becomes available immediately after the cube has built.
If you want to open a cube in Excel that you have already or previously built, then the menu option "Cube", "Open a pre-built cube in Excel" provides this capability, details of what to do when you get there are available in the Opening Pre-built Cubes in Excel help topic.
Alternatively, if you would like to know how to achieve the same from within Excel 2007, here are the details.
Open Excel. On the Data tab, in the Get External Data group, click From Other Sources, and then click From Analysis Services. Enter The Analysis Services server name entered in the Settings screen and any required logon credentials, and click Next. Under Select the database that contains the data you want, select the database name used in the Cube Design screen. Make sure that Connect to a specific cube or table is selected, and then select the cube name used in the Cube Design screen from the list. Click Next. Optionally alter the file name and description settings and click Finish.
Keep the default Import Data wizard settings to create a pivot table report and click Ok.
Select the Rows, Columns and Data and position them using the PivotTable Field List to analyse your data in Excel.
