If everyone one on earth lived a lifestyle like that of Americans and Canadians, the world would not have the resources to support the population we currently have.
If everyone on earth lived a lifestyle like that of a vegatarian Indian living in a small shanty style home, the world could probably support more then double the number of people we currently have ( the US could under such conditions support a population of over a billion people easily)
It truely depends on the living conditions that people would generally want to live under.
I would rather live a lifestyle similar to that of what we have in Canada and the US then of the poor in India, I bet the poor in India would generally live a lifestyle similar to that of what we have in Canada. So under that premise, we are overpopulated