Can someone explain the ending for me?

Think "the driver" was something more like "the power of the VHS-tapes" that has been shown in one form or another in all three wraparound-stories and AFAIK, it hasn't been explained, nor do I think we'll ever find out, since making a solid mystery is really easy if you just ignore to ever make up an explanation that would actually work [great].

My best guess is that some energy from all the evil sticks with the recording, and that energy wants to bond with more of the [similar] energy, and that energy isn't so much sentient as viral, thus it infects tape-hoarders (hubs/transportation), corrupts some - like the girlfriend- to be a part of it (new/more energy) and just generally acts evil because that's what it is - the cop, biker, etc. that got killed.

Like I said, the hard part of making a mysterious plot is having a great reason for everything that happens. My thoughts on it aren't worthless, but that would basically mean that V/H/S's story is a revamp of how "The Ring" works in the original novels.