In the Workbook code, put something like this:
Private Sub Workbook_Open()
On Error GoTo errorSheets(Format(Date, "dd-mm-yyyy")).Select
Exit Sub
error:MsgBox ("Today's sheet doesn't exist")
End Sub
This will select the sheet named as today's date (eg 29-01-2008) or issue a message if it can't be found.
HTH,
Vindaloo