Using the SQL Server Enterprise Manger, create a new job, alter script in the job step with the detail below and then schedule the job. Each time that the job is executed, the backup file will be created with the same name and will overwrite the previously written backup file.
exec master.dbo.xp_backup_database @database = 'Northwind'
,@filename = 'D:\backup\Northwind.BKP'
,@backupname = 'Northwind backup'
,@desc = 'Backup of Northwind'
,@init = 1
,@logging = 0
,@with = 'SKIP'
,@with = 'STATS = 10'