Oh man, this was ages ago, so I don't even know if it is still available on the web.

The best I could found is a similar tut where they are adding other features to notepad:

http://www.kaoteq.com/sites/fravia/fravia-darkridge/nnhnpad....

This brought me lots of memories, learning from +ORC, tKC and +HCU was the bomb back when I was in University.

I could not find the one specific for adding line numbers though.