I previously showed you (without a screencast) how to make NP++ default in XP. Of course, people have successfully done this for W7/Vista as well, but the various tutorials I saw were all a huge pain in the ass. Except for one: a comment on a more-complicated method. I made the following short screencast to demonstrate that method. This one has the advantages of being easy to reverse, easy to do, and not in any way intimidating!
I also have a post on using regular expressions in NP++, if you’re into that sort of thing.