Peter,
Absolutely, I wrote a procedure that I call, called KillExcel and I call
this after every instance of an excel object being opened.

   Public Sub KillExcel(ByRef objws As Excel.Worksheet, ByRef objWb As
Excel.Workbook, ByRef appXL As Excel.Application, _
                           Optional ByVal strSaveAs As String = "", _
                           Optional ByVal bSave As Boolean = False, _
                           Optional ByVal bProtect As Boolean = False)
       Dim proc As System.Diagnostics.Process
       Dim intPID As Integer
       Dim intResult As Integer
       Dim iHandle As IntPtr
       Dim strVer As String

       If bProtect Then objws.Protect("password", True, True, True)
       If bSave Then
           appXL.DisplayAlerts = False
           objWb.SaveAs(strSaveAs)
           appXL.DisplayAlerts = True
       End If
       If Not (objws Is Nothing) Then
           System.Runtime.InteropServices.Marshal.ReleaseComObject(objws)
'You must call this if you are using Excel 11.0 Object Library
           objws = Nothing
       End If
       If Not (objWb Is Nothing) Then
           System.Runtime.InteropServices.Marshal.ReleaseComObject(objWb)
           objWb = Nothing
       End If
       If Not (appXL Is Nothing) Then
           appXL.Caption = "TRAKKER Excel"
           appXL.DisplayAlerts = False
           strVer = appXL.Version
           iHandle = IntPtr.Zero
           appXL.DisplayAlerts = True
           appXL.Quit()
           If CInt(strVer) > 9 Then
               PostMessage(appXL.Hwnd, conWM_QUIT, 0, 0)
           Else
               iHandle = FindWindow(Nothing, appXL.Caption)
               intResult = GetWindowThreadProcessId(iHandle, intPID)
               proc = System.Diagnostics.Process.GetProcessById(intPID)
               proc.Kill()
           End If
           System.Runtime.InteropServices.Marshal.ReleaseComObject(appXL)
           appXL = Nothing
       End If
   End Sub