How to Create a Richtext Editor (WYSIWYG HTML Editor)
http://devedge-temp.mozilla.org/viewsource/2003/midas/01/index_en.html
This is a great tutorial on creating an HTML editor. The editor works in both IE and Firefox. Also it very easy to use, using simple JavaScript functions and doesn’t use a bunch of files to work.
The website source on this is Modzilla, so it’s creditable.
Also here is where you can see a list of JavaScript commands for this type of editor:
http://msdn.microsoft.com/library/default.asp?url=/workshop/author/dhtml/reference/commandids.asp