Here's two things to try.
Install "alltray" then change your korganizer startup command to:
I don't know how well alltray worked in Kubuntu Lucid, but it's crashing on me in Kubuntu Maverick-(aplha), so I have another idea below.
KDE has a native application called ksystraycmd that can be used.
See which command works better for you. You can also type "ksystraycmd --help" in the Konsole (terminal) to find more options for ksystraycmd.
ksystraycmd --hidden korganizer
ksystraycmd --hidden --startonshow --keeprunning korganizer
Hope this helps.