Are you using your won HTML Template or using the HTML Exporter ?
The HTML Exporter does this automatically:
Attachment:
File comment: Screenshot
Screen shot 2010-11-26 at 11.38.14.png [ 20.09 KiB | Viewed 476 times ]
Also you can enable 'live diagrams' so the diagram elements themselves become clickable:
http://merlinscave.info/Merlins_Cave/Ti ... tures.htmlOther than that you could put a Hyperlink in the description field for the Action that points to the Sub Activity
Cheers
Andy