First, I think that a personal learning environment is what an individual accumulates, constructs and experiences themselves: comprising their face to face experiences in elective small groups and formal activities such as lectures and tutorials; their desktop access that might be bookmarks, an online desktop such as Netvibes, Pageflakes, iGoogle; and whatever formal learners ar offered by way of Virtual Learning Environments and resources.
A personal learning network is a network of people and things that generates and sustains learning for an individual. Connectivism is, I think, looking at learning within networks of people and things, as something that emerges from this. My own take on this is that the agency of people , what they do !!, is very important alongside what they find, supplement, amend by way of content/things/etc.