I have to credit "vbslammer" with the following, which worked great for me with respect to opening an Excel Document from Access (although I am still struggling with working with an already open Excel document).
Public Sub OpenExcel()
On Error Resume Next
Dim xl As Excel.Application
Dim wb As Excel.Workbook
Dim sht As Excel.Worksheet
Set xl = New Excel.Application 'instantiate Excel
xl.Visible = True
' use Excel's built-in open dialog
xl.Dialogs(xlDialogOpen).Show "C:\*.xls"
Set wb = xl.ActiveWorkbook
' put appropriate sheet name/index here.
Set sht = wb.Sheets(1)
' tinker with range properties
With sht
With .Range("E20", "G20"

.Merge
.Value = "Merged Cells"
.HorizontalAlignment = xlHAlignCenter
.Font = "Comic Sans"
.Font.Size = 18
.Font.Bold = True
.Interior.ColorIndex = 27
End With
.Activate
End With
' do more stuff...
End Sub