since it is plasma you can’t add desktop folders in kde4
depending on which version of kde4 your running you can add a widget that shows folders etc… and create them
Go to Dolphin in your /home find Desktop open it right click in there you’ll get to create a “new folder” in there. Then from the /home/Desktop drag & drop your “new folder” to the desktop.
If all has gone well you’ll have “new folder” in both you/home/Desktop & on the desktop you look at all the time.
that version of kde4 doesn’t have the folder veiw have to have 4.1 beta 2 if im not mistaken
take a look at this months screenshot thread and you will see what i mean