Nothing. I don't get the script editor window, which is why I assumed that I needed the full copy of VS to use scripts.
Add a Script task to the design surface
Double click to get the script task dialog box
move to Script in the left pane
Click on Design Script button
The dialog box closes and returns me to the design surface with the script task having focus with its drag handles.
FWIW I don't like script tasks as I think that they obfuscate what is happening (and VB.net scares me!) . I would prefer to use an alternative where possible, even if it is not so efficient.