Hi.
I want to share the method for putting windows to system tray on KDE (3.5.x) startup. The method (solution) came when kmix didn't start with kde on my computer, not even with session restore. Session restore works, since skype for example always starts when I log in (after I logged out with skype turned on).

So I searched for solutions, and here it is:
Write a small shell script, which looks like this:
Save the script, and make it executable. Now copy/move the script to "/home/user/.kde/Autostart" , and voila we're ready.

As you can see the script is written for kmix but I think it will work for other apps too (which start with a system tray like kmix), just replace the kmix parts.

To identify the window you want to hide (kmix-mainwindow#1 in this case), open the KDE ControlCenter --> Desktop --> Window Specific Settings.

Here click "new..." and than search for the "detect" button under the "window" tab. A cross will appear. Use Alt+Tab to roll for the opened window you want to hide at startup (you have to start it first), and than click onto this window with the cross. A new window will appear with some info. You will need the entry of the second line. This is kmix-mainwindow#1 for kmix for example.

This is all you need.
Have fun!

EDIT: This was my 400th post! WOW. Hope it's useful...

ksystraycmd allows any application to be kept in the system tray.