I always forget where the option for this is as you normally only need to turn it on once and it's done in each application but I just needed to write a quick Macro to outlook so I needed it.?
If you need to make a Macro or do some VBA work in any of the office applications you add the developer toolbar by going to File -> Options -> Customize Ribbon -> under the Main tabs listbox, check Developer. Done!
You can also open the VB window by pressing ALT+F11 (incidentally this works in many Autodesk products and in Visual Studio too :-) )