Everthing the other folks said.  However, if you are looking to get 'Hayden' or any of the other 'realistic' faces of real people, you should go to DeviantArt and read the short description by Fygomatic concerning his technique of modeling and texturing.  It is in the comments section of his gallery.  Then you will need the two elements you cannot buy (at least I cannot--time and talent).

I think the guy is amazing.