I came across this interesting page which discusses adding a WYSIWYG interface to Quanta Plus. The page was written in March this year, and I'm not clear on how far this has got, but it looks very much like what I was looking for.
They discuss the importance of generating clean, W3C compliant code and also mention of PHP scripts. I'll be looking around but does anyone know if this got any further?
http://members.shaw.ca/dkite/mar212003.html
-- Ben "tola" Francis