Google Sites Help

Just click "Edit" to edit a text page and select "insert" > and the object you wish to insert to include a read-only version of the object. When the embedded object is updated at its source and published, it is updated automatically within Sites. To ensure your site always contains the latest version, set the object to automatically republish changes.

Please be sure that you're using the "Insert" function in order to embed objects. Cutting and pasting the embedding won't work as it will be stripped out.