I start two or three Excel 2003 sessions at the same time so that I can use multiple displays and work on a couple of tasks at a time. To start a new Excel session, you launch it from the Windows Start menu instead of opening an Excel file in Explorer (opening an Excel file loads it in the active Excel session). A new Excel session has, by default, a Task Pane (a panel titled 'Getting Started') and a new workbook, both of which I rarely use, so I close them before opening an existing file.
If you don't want the Task Pane opened by default, open Excel's Options dialog and uncheck View, Show, Startup Task Pane.
If you don't want a new workbook by default, create a new shortcut to start Excel with the
/e argument and open Excel with that shortcut.