General contractor vs Project manager

[Tyrone L. Robinson]

As a kid I was obsessed with shows like This Old House (before HGTV) and I love all the flipping shows on tv right now.

I'm wondering what are the differences between a General Contractor and a Project Manager on a house flipping project? 

Are there always both on a house flipping project? And how do you learn how to become a GC or PM for house flipping projects?

Listening to the BP Podcasts I always hear how hard it is to find a good General Contractor. I haven't heard as much about Project Managers and I think I may favor that over General contracting since I don't have skills in construction or plumbing or electrical or anything like that.