Making Spawnpoint Script

I'm trying to make two spawn points. They are both empties that spawn two types of power-ups. How can I make them constantly spawn a prefab at regular intervals?

Probably what you want:

http://unity3d.com/support/documentation/ScriptReference/MonoBehaviour.InvokeRepeating.html

or,

http://unity3d.com/support/documentation/ScriptReference/Coroutine.html

what is the problem then dont you know how to script the timer or how to instentiate objects?explain your question a little bit more...