Use Kontact through NX
From Kolab Wiki
It may be possible to use Kontact on windows/mac clients using NX - http://www.nomachine.com or FreeNX
With version 0.3.1 of FreeNX it is possible to run kontact in a "single window" - this is almost the same as having it installed locally. I used the howto [here] to get freenx installed (installed the NX component with apt on suse).
A nice aspect of NX is that the most recent version (1.4) supports persistent sessions.
To run kontact in single window mode, it needs to not fork, so make a new file in /usr/bin (or wherever you want) and put in:
then make it executable:
chmod 755 /usr/bin/kontact-nofork
(It seems there may be trouble with spaces, not sure). In the client, under DESKTOP choose UNIX, Custom, then click SETTINGS. In RUN THE FOLLOWING COMMAND, put /usr/bin/kontact-nofork (or whatever you made it)
This worked with problems on WinXP SP2. The client seems to be a bit laggy, and I had problems with nxclient being a bit of a cpu hog, also there are problems with kdewallet, Korganiser popups.