You can just create an autorun.inf file in Notepad and save that to the root of your CD project. Just set the "open" line to the name of your HTML file:
Code:
[autorun]
open=filename.html
Note that if you use the Plexus plugin (i.e. the normal Opus web plugin) then your end users will still need the plugin installed; in which case it's probably simpler to just use a standard Opus executable, rather than requiring the user to install any new software.
If you use the Flex (Flash) output this is not likely to be a problem, but you will have to cope with the limitations of the Flash output (no video, no external windows, etc).