Many experts on artificial intelligence state that when computational power exceeds that of the human brain, we will have computers smarter than humans. But how can we program something smarter than ourselves?

This is something I've never been able to get my head around. I've heard that currently our supercomputers are about as smart as a "mentally chellenged cockroach" (quoting Michio Kaku here) and that some day in the future (if we figure out molecular/quantum computing) our computers will be as smart as a human.

This notion seems backed by many credible people such as Ray Kurzweil, Steven Hawking and the aforemention Michio Kaku, but I don't understand how we could do this. A computer has to programmed, so surely despite its raw computational power it is still is limited by its programming (which is done by a human).

So basically my question is: Even if we have enormous computational power, how can we program a computer to be smarter than ourselves?

Thanks, hope this is clear