You cannot read your StarCalc 5.0 files (.sdc)
with Excel 2000, but you can create Excel 2000 files (.xls) and
Excel 2000 templates (.xlt) using
File, Save As from  Star Office 5.0 which is available free from
http://www.sun.com     It is a very large [76.8MB download, Free],
http://www.sun.com/products/staroffice/5.2/   limited to 32,000 rows,
very compatible with Excel.

This is similar to conversions involving older versions of Excel
you cannot create an Excel 2000 file from Excel 95, but you can
create an Excel 95 file from Excel 2000.    Most spreadsheet
software can create an Excel file even if it is an older version of
Excel that it creates.