You can set up KDE to only display a blank desktop (no icons, panels) and probably disable the desktops context menu if you wanted and make it auto-launch the browser on login. Disable all the other tty's in /etc/ttys and (maybe) run X on the first, I dunno never tried it.
As far as Kiosk mode, this is some of the documentation for KDE and Kiosk mode.
KDE System Administration/Kiosk/Introduction
Kiosk Admin Tool
I think Antik or some one else posted a guide about it last year.