I think what most people don't have in mind here to is that it's prefereable to learn and use cross-platform tools over platform-specific tools. If you use only Notepad++ and you find yourself at a linux or a mac computer, what program do you use then? Dreamweaver is Windows/Mac and things like jEdit are for all three. It's best to spend your time learning something that will be free and available no matter what situation you find yourself in. Another plus is that way you aren't trapped in what they call 'vendor lock-in' where you have been kept ignorant by one vendor and because of that you can only accomplish your task in their software, so every time they release a new one you have to buy it or you can't continue to do your work. How anybody manages to do any serious development on a Toy Operating System like windows is beyond me, if I were you I'd seriously consider learning some cross-platform tools and going to apple.com for your next computer. If you try using a mac and you don't like it, there's nothing stopping your from dual-booting it with windows and using that for your development again, but I doubt once you learn how to use mac that you'll go back. Same deal with linux.
I use textpad, have been using it for years, it's absolutely awesome! Here's the link http://www.textpad.com/
I generally just stick to Notepad++ or the odd time I'll maybe use Dreamweaver for quickness. It depends on what I want do. If I'm coding PHP sections I normally do them by hand in Notepad.
Notepad++ is pretty good and open-source! You can download it from here: http://notepad-plus.sourceforge.net/uk/site.htm
The original notepad will allow you to edit and write php files? I would however recommend using Dreamweaver or Notepad++
The reason why I do this with Dreamweaver, is that it uses colours which makes the script a lot easier to read.