Notepadd++ is one of a handful of text editors I routinely use. It has worked successfully on Vista 64bit & now on Windows 7 64bit. Unfortunately, something keeps the right click shell integration from installing correctly.
The good news there is a simple registry hack to add the functionality back in:
http://blog.donnfelker.com/post/Notepad2b2b-Shortcuts-Vista-64bit-Update.aspx