In Excel 2003 there appears to be no command available through the menus. However, I have a VBA macro as part of an "auditing" workbook that unhides all hidden worksheets:
Sub showAllSheets()
Dim sheet As Object
Application.ScreenUpdating = False
For Each sheet In ActiveWorkbook.Sheets
sheet.Visible = True
Next sheet
End Sub
With some more work you could have a similar command that would load a dialog with a selection list which would list all of the hidden worksheets and then allow you to select multiple sheets to unhide at once.