Hello,
I just installed Kubuntu 9.04 and I tried to configure the network.
Internet does work but I can't change the options so that it doesn't use DHCP, indeed when I went through System Settings>Network settings>Network Managment>add, the changes I made hasn't got any effect.
So, what did I do wrong ?
Thanks

This plasmoid is still under development at this time, despite being released with Kubuntu 9.04. It is likely that static IP addresses have not been implemented at this time.

Is there an other way of configuring that ?

I would recommend switching to wicd in the meantime which is a light python based network manager. It has a Gtk frontend unfortunately, but it is very reliable, and is the only Gtk application I use.