If you do upgrade to KDE-3.5, one thing to note is that Kubuntu normally has their *own* menu item for System Settings, which is supposed to replace the KDE Control Center. But when you go to KDE-3.5, that particular component is no longer as functional as the real thing --> Eg. when trying to select a keyboard layout variant.

So you may also then want to Right-Click on System Settings (from the K menu), and do edit item, and change the Command it runs to be /usr/bin/kcontrol. Or do what I did, and just create a second menu entry, for KDE Control Center (/usr/bin/kcontrol).

Cheers