First, you may be interested to know that there's a newsgroup just for
Mac XL:
microsoft.public.mac.office.excel
Upgrading to Leopard, by itself, should have had zero effect on how a
file displays on opening. It could be that you deleted the standard
font, so that XL is substituting a font with different metrics. Or you
could have changed screen resolutions such that the sheet is limited.
You don't say what "normal sheet" means to you, so I don't know what you
think it should look like, but the best way to get a consistent view is
to create a default workbook.
Open a fresh workbook. Size it the way you want, and change formatting
to suit your tastes. Save it in XL's Startup folder (by default
HD:Applications:Microsoft Office 2004:Office:Startup:Excel:
though you can change it in XL's Preferences/General dialog).
The file must be saved *as a template* with the name "Workbook" (no
quotes, no extension). From then on, the File/New command will use that
workbook as a template for your new files.