I recently came across an interesting project which required to open an HTML file inside the CD-ROM using the default browser on the users side. There are two ways, both are equal in terms of complexity and flexibility.
This uses the standard ShellExecute command.
[autorun] shellexecute=index.html label=Autorun HTML action=Open index.html
This method requires you to download a small executable and put it within the contents.
[autorun] open=autorun.exe index.html label=Autorun HTML action=Open index.html
Please note that the above examples only shows a few of the options you can use in a Autorun.inf file. For other possible entries, please refer to MSDN.