Welcome to the forums,
Neither of the two RFE links mentioned in the above threads are implemented yet for Zimbra Desktop. By your wording I'm unsure if you're saying you can't find any sharing in Zimbra Desktop or the ZCS advanced webclient.
Bug 26170 - Cannot accept the share calendar using Zimbra Desktop
Bug 19182 - Support sync'ing shared folders (mail, contacts, calendar...) in zimbra desktop
(Chimaster above you was having a different issue with the accept buttons showing up in the web-client as mentioned in another thread, but I'm unsure if he's seeing that after his upgrade from 5.0.3 to 5.0.8)