Other than openoffice, can you suggest a light free viewer for excel files?
I myself use OS X's Quick Look. I think it's good enough.
Just select your xls (or xlsx) file and do one of the following:
and the file will be viewable in a separate window. Press Space again to close.
Quick Look can also be opened in full screen by pressing ⌥ Space or ⌥ ⌘ Y in the Finder. Press Esc to exit full screen.
Apple Numbers can open Excel files. Numbers launches faster than Excel, however it still takes forever and it's not free.