PostgreSQL dump/restore from 8.4 to 8.1 in a shell script
You can drop the table (and dependent DB objects) with the pg_dump parameter --clean, from the pg_dump manual:


  -c, --clean
     Output commands to clean (drop) database objects prior to
     outputting the commands for creating them. (Restore might generate
     some harmless errors.)


So in your case this should be

D:\PostgreSQL\8.4\bin\pg_dump -U postgres -p 5433 --clean -t my_table myDB &gt; D:\backup\myFile.sql


you should then be able to restore the dump file with your current restore command in the cron job.

Hope that helps.