This is from the Word help file:
Dim MyXL As Object ' Variable to hold reference
' to Microsoft Excel.
Dim ExcelWasNotRunning As Boolean ' Flag for final release.
' Test to see if there is a copy of Microsoft Excel already running.
On Error Resume Next ' Defer error trapping.
' Getobject function called without the first argument returns a
' reference to an instance of the application. If the application isn't
' running, an error occurs.
Set MyXL = Getobject(, "Excel.Application")
If Err.Number <> 0 Then ExcelWasNotRunning = True
Err.Clear ' Clear Err object in case error occurred.
' Check for Microsoft Excel. If Microsoft Excel is running,
' enter it into the Running Object table.
DetectExcel
' Set the object variable to reference the file you want to see.
Set MyXL = Getobject("c:\vb4\MYTEST.XLS")
' Show Microsoft Excel through its Application property. Then
' show the actual window containing the file using the Windows
' collection of the MyXL object reference.
MyXL.Application.Visible = True
MyXL.Parent.Windows(1).Visible = True
Do manipulations of your file here.