I was recently reviewing different WYSIWYG controls. Here's a list of some:
http://www.hotscripts.com/JavaScript/Scripts_and_Programs/Content_Management/
Most require IE 5.5 or greater but some like
http://www.interactivetools.com/products/htmlarea/
are starting to support Mozilla on all platforms. I was planning on adding one of these to ETP for a project I might have to do soon and it seems straightforward to me but that's just from a cursory glance at the code.
