Excel 2003 — any version of Excel, actually — is about creating spreadsheets (worksheets) contained in workbooks. To navigate around worksheets and workbooks in Excel 2003, use these keyboard shortcuts:

Press To
Ctrl+Page Down Activate next sheet in the workbook
Ctrl+Page Up Activate previous sheet in the workbook
Shift+Ctrl+Page Down Select current and next sheet in workbook
Shift+Ctrl+Page Up Select current and previous sheet in workbook
Shift+F11 or Alt+Shift+F1 Insert new sheet in workbook
Alt+OHR Rename current sheet (Format→Sheet→Rename)
Alt+OHH Hide current sheet (Format→Sheet→Hide)
Alt+OHU Unhide current sheet (Format→Sheet→Unhide)
Alt+OHT Select new color for sheet tab (Format→Sheet→Tab Color)
Alt+EM -Move or copy current sheet in workbook or to new workbook (Edit→Move or Copy Sheet)
Alt+ED Delete current sheet (Edit→Delete)