Hello Mohammed,
Thank you for your question. You can do this using the TinyMCE editor in Joomla 2.5, here is a link to our article on the Joomla 2.5 Editor.
First, go to the Global configuration, and choose Default WYSIWYG, then TinyMCE. Change the functionality from simple to extended and save.
Now, when you are creating an article, there will be a button available in the toolbar to "insert edit embedded media," use this tool to insert your .swf file.
If you have any further questions, feel free to post them below.
Thank you,
-John-Paul