Notepad++ has some kind of shim so that, while not physically replacing notepad, N++ will be invoked for (most) uses.
I second that. the latest version of Notepad++ (4.02 IIRC) is really HUGE improvement over previous versions - on the one hand it can be used as a simple notepad replacement.
But on the other, if you change certain Preferences/Settings, it should become an obvious choice for your default programming editor for markup and scripting languages. HTML, XML, CSS, PHP. Apart from those, it supports practically every programming language (at least 3 you have never heard of
) and is FAST and has some *exceptional* text manipulation plugins that help you reformat your text (upto 10s of MBs) in *one single command/click*.
The latest version has an explorer sidebar, favorites, hex editor and function list.
The Text FX Viz plugins are mighty impressive - of course, everything is free GPL. If you just want a notepad replacement and you *dislike* feature-packed software, I suggest editor2, amazing stability and several smart, quick features.
Really worth trying out.
Both have instructions on how to replace Notepad as the default system editor.