[throwaway420]

Unless you're planning on hiring the Inception people and literally erasing this idea out of their brains, you would never be stealing their idea - you'd be copying it. They still have their original idea and can build anything they want based on it.

You should probably talk to the founder about this issue first.

If you feel bad about this situation for any reason, you might consider hiring them to do some consulting work for you on this project, whether now or some point down the road. This provides just some of the following benefits...

* An extra learning experience for them where you can set them on the right road to performing some tasks they otherwise never would have thought of * some extra compensation that they would have otherwise never had an opportunity to get * an opportunity to really gauge their competency and see if they can have a major future role with you.