The best practice in this field is to make your game framerate independant, as you cannot manage every type of computer. This tutorial
can show you how to do it.
This way, people with low config won't suffer from it playing your game, and people with higher will enjoy it too.
If you still want to slow down the rendering, I'm not sure there is a way. It would be in the project properties I think, and I can't see anything like this.
Edit : ninja'd ^^Guizmus2013-07-17 21:57:04