You can continue using Linux. I would recommend remastering KNOPPIX or building your own Debian live-cd, but this is a matter of choice, so you can use any distro you want. OpenSUSE Build Service is quite interesting, too.

You can install any packages you need, place your site files, install the webserver and add an auto-running script (for example, in /etc/skel/.xinitrc) which launches the browser you installed at http://127.0.0.1/.

The user will just need to place the CD in his drive and reboot.