When you try to insert code (HTML, PHP etc) into content, the WYSIWYG editors strip out any code you enter into content. To get around this problem you need to turn off the WYSIWYG editor temporary.

You should not change the settings in your configuration.php to No WYSIWYG. No need for that and you want other users still being able to use the editor while you doing admin stuf? So you go to your User Account in the Admin backend, set in your account the editor to "no WYSIWYG" (top right).

Go to the content, insert the code/cript and save the content item. When finished inserting you can go back into your account and turn the WYSIWYG editor back on again.

However, you will need to remember that, if you go back any time in the future to edit that content item, you will need to turn off the WYSIWYG editor otherwise the code will be striped out when you save the content item.

Search the Extension directory. A couple of very cool mambots/plugins are now available to assist you without turning off the editor! Of of those Extesnsions is the JCE-Editor which has a [show/hide] function in editor pane allowing you tio easy insert javascript etc. Extension is free! http://joomlacontenteditor.net