Save the excel file as a generic name,like file2import.xls.
Link the file as a table.
Make 2 queries,
1 query to add new records that don't exist.
1 query to update existing items (if needed).
Put the queries in a macro.
So the workflow would be:
1.Get new XL file,save and overwrite file2import.xls.
2. Run macro.
Done.