[mmorse]

If you are indeed asking about nested cal folders (glancing at your other thread Imbrication of task's lists) then: http://www.zimbra.com/forums/announcements/18454-5-0-6-out.html

I show you as ZCS Version: Release 5.0.5_GA_2201.UBUNTU6 NETWORK edition

These we're completed for 5.0.6:
Bug 8765 - Allow hierarchical organization of calendars into subfolders on Zimbra web client
Bug 5997 - calendar subfolders can disappear
Bug 6410 - departmental calendar grouping

Open enhancement: Bug 27211 - Support user creation and moving of nested calendars