kolab clients

[=?koi8-r?Q?=22?=Igor Shmukler=?koi8-r?Q?=22=20?=]

What clients than be used to take exploit such features as IMAP and calendar?
We have mixed environment. Some people are happy with Outlook 2000/XP on Windows, as I understand Toltec connector is your friend there. Although after we installed it on test workstation, Outlook 2000 started crashing every so often. Has someone experieced something like this? I personally like my OSX workstation, but I could not find a client with a calendar. (even though I have iCal that should be using the same format to store data) I thought Mozilla had one, but I could not find calendar features in 1.6 bundle I installed. Is KDE+Kmail the only alternative to MS Outlook?
What webclient is best for both calendar and email?
Thank you very much,
IS.