Joomla Can't insert code in article need quick help

I am trying to insert either php code into an article in Joomla or some <iframe>some code here</iframe> type code into a Joomla article but for some reason I get a 404 page error. I have other Joomla websites and have never had this problem before. I have three forms that usually use the <iframe> type code but this version of Joomla 1.5.8 will not let me. The budget is $30, if you know what you are doing it should be easy. Perhaps I need to modify the server or .htaccess file, you will need to tell me what must be done. Once you are finished please show me what was done to make this happen.