You can use the 'EnableEvents' property to prevent the Workbooks_Open event from triggering when you open the workbook. You want to re-enable events after the workbook has opened by setting the property to True. Here's an example.
Code:
Sub OpenWBTest()
strPath = ThisWorkbook.Path
strFileName = strPath & "\" & "ONOpenTest.xls"
Application.EnableEvents = False
Workbooks.Open (strFileName)
Application.EnableEvents = True
End Sub
As shades hinted, you can do this without opening the workbooks and bypass the on-open events. The way I know of to do this is by using ADO to retrieve the worksheet data into a Dataset. ADO can be tricky to set up. Opening each workbook will probably be easier for you and can work well.