ER/Studio includes a basic ISQL editor, which is ok, but if you want to have feature rich SQL IDE to help write robust SQL then you can choose to integrate with Rapid SQL.
To change the SQL IDE change the path in Tools | Options | Tools within ER/Studio and point it to Rapid SQL:
Now any time either of the application wizards generate any SQL code (i.e. compare and merge, generate database), the code will launch in Rapid SQL.
Find out more about Rapid SQL here: http://www.embarcadero.com/products/rapid-sql