I am also using PHP iCalendar, iCal, and Mozilla Sunbird (on my PC at work).
Regarding the "2 calendars max", are you using the 2.0 beta version? I have successfully gotten more that 2 calendars to be displayed.
http://www.baizman.net/icalendar
There are some wierd inconsistencies between Sunbird and iCal. I don't know who is "right" according to the IETF spec, but I do know things are different, annnoyingly so.
- Sunbird creates all events marked as "Private" by default, so you need to make sure that the checkbox is left unchecked before publishing and/or exporting your calendar.
- Sunbird creates all events with a "Tentative" status by default. iCal by default creates events with no status. These events appear to Sunbird to be "Tentative", because there is no option for "no status".
- Sunbird uses Universal Time for events. However when copying events from a Sunbird-created calendar to an iCal calendar, the events don't have a time zone associated with them, so they show up at the wrong time until you manually add a time zone to that event.
Marc