I use joomla to manage a website... and i am developing a stand alone php application that will insert and modify data into the tables that are used by joomla to store the
You should not need slashes. The only thing that will cause a problem during normal inserts is the quotes, and mysql_escape_string() should handle that excepting charset issues. Try mysql_real_escape_string() as well.
Also, note that storing raw user-supplied HTML in the database can lead to security issues. Consider using something like bbcode or markdown instead.