Just to clarify a bit more, documentation on how to integrate HTML-Kit Tools with the XAMPP server package.
There are a couple of ways to do this.
You can simply open a document that you want to preview through XAMPP
and select "View > Preview > Preview server-side script" from HTML-Kit
Tools main menu.
To make it easier to manage multiple sites though, I'd create a project
("File > Projects > New") and add the local folder where you keep XAMPP
hosted files. In "Add Local Folder" dialog, change to the "Preview" tab
and set the XAMPP server host so that when you preview files from that
folder they'll automatically go through XAMPP web server.