I am looking for pay-per-view software to run on  my how-to video website.

I would like the software on a linux server.

and

a complete system which includes software and hardware

You could always use some anti-leeching script to dynamically create a
link to content, and somehow attach a little paypal to it, it wouldnt
be hard to do if you could find someone to code it for you.

There was a post on Slashdot about this today:

Apparently, Google will be offering pay-per view video services.

http://slashdot.org/articles/05/06/27/1126237.shtml?tid=217&tid=129&tid=1
It references http://battellemedia.com/archives/001658.php as the source.

You can check it out at:
https://upload.video.google.com/