To use ktalkd, you need a talk client. The text-based talk is available on most Unix systems. Try talk your_username to see what happens when you receive a talk request. You can also try the answering machine the same way : initiate a talk to yourself, ignore the announcement twice, and you'll see the answering machine.
There is a talk client with a graphical interface for the KDE, ktalk. It's not yet shipped with KDE packages, but you can find it on ftp://ftp.kde.org. It should be in ftp://ftp.kde.org/pub/kde/stable/latest/apps/network
The announcement dialog box is trivial : respond or ignore.
The configuration dialog should be rather straight forward, except for setting up a forward to another user (or even to another host).
None is perfect, they all have pros (+) and cons (-).
FWA : Forward announcement only. Direct connection. Not recommended.
(+) You know who the caller is, but
(-) Caller will have to respond to an announcement from you. Annoying.
(-) Don't use if you have an answering machine on your 'away' location. (The answering machine can't popup an announcement, it would be confusing!)
FWR : Forward all requests, changing info when necessary. Direct connection.
(+) Caller won't know that you're away, but
(-) You won't really know who the caller is - only his username, (so you might see "talk from Wintalk@my_host")
FWT : Forward all requests and take the talk. No direct connection.
(+) Same as above, but also works if you and caller can't be in direct contact one with the other (e.g. firewall).
(+) You'll be told who's really talking to you when you accept the talk
(-) But as in FWR, you won't know his machine name in the announcement
In short, use FWT it you want to use it behind a firewall (and if ktalkd can access both networks), and FWR otherwise.