Are you using 2009 still with KDE 3, or has it been updated to KDE 4?
In KDE 3, it can be set from within the KDE Control Center (see http://www.pclinuxos.com/forum/index.php/topic,70220.msg577118.html#msg577118
For KDE 4, I couldn't find it in a centralized area, but when I ran krfb
from the konsole, it opened a window to manage invitations from. On there, there is a "Configure" button.
On the config window, go to "Security". Add a check to "Allow uninvited connections", and then remove the check from "Ask before accepting an uninvited connection". I would strongly
recommend a password.
Hope that helps.