RTM integrates nicely with Google Calendar (Remember The Milk - Services / Remember The Milk for Google Calendar). Has anyone gotten something similar working with Zimbra Calendar?

RTM will serve todo lists as ICS files and I've tried subscribing to them from within the web interface but I see nothing on my calendar. It allows subscription to both "iCalendar" and "iCalendar (events)". (What is the difference?). Regardless, neither RSS feeds seem to contain my data, even after I've published the lists to be viewable to the public. I've been looking around RTM's Help site (Remember The Milk - Help / FAQ / iCalendar Service). I think I might have missed something obvious.

I'm posting on RTM too (Remember The Milk - Forums / Help / Zimbra Calendar Integration with Remember The Milk), as it seems to be more of a question for them, but Zimbra forums have been really helpful and I thought there might be someone on them who uses RTM. Thanks.