There is a kde software package that's especially being made for webdesign. Just install the kdewebdev package. It will install quanta plus which has wysiwyg support and good coding support (syntax highlighting and great code-completion that is somehow quite intelligent). It also has php support and supports php debugging.
Another package you could try is eclipse and the phpclipse plugin. But that could also be overkill.
ps. You can find more about quanta here:http://quanta.kdewebdev.org/