SQL Database backups are meant to be used for disaster recovery, not individual site collection restore.
However, if that is all you have to work with then you will need to build out a new SharePoint environment similar to a DR scenario (attach the content database from sql database backup).
Once you got your new SP DR environment up and running with your sql backups, you have to backup and restore the site using the stsadm -o backup/restore command (backup from from DR env, then restore to production).
Very time consuming and difficult.
