effects - How were Hiro's time halting scenes filmed?

In many scenes in Heroes, we witness Hiro Nakamura display his ability to stop time:

However, also in these scenes, we witness him interact with the scene, whether it be interacting with stopped objects or just to move around.

My question is how was this accomplished? Is it a simple CGI trick or a combination of that with actors/extras having to remain REALLY still?

Answer

One of the DVDs from the series has an excellent special feature showing the process used. It was often a combination of Green Screen/CGI and staged actors and props. So to answer the question it is a fusion of both.

The example shown on the DVD is a scene in the street where he's moving through a crowded shopping district and rescuing a child from an accident.

Note: No CGI trick is "Simple" ;)