There is an URL about that but the system does not allow me to post it directly. Just google for sujet-979-having-a-static-ip-address-under-ubuntu-8-10 .
Quoted from another posting:
The Network Manager actually has some support for static IP settings already, but the distro specific backend has to support it. Fedora, SUSE, and Debian support it. But Ubuntu decided to make NM ignore _any_ interface that you have already configured in /etc/network/interfaces. Therefore, to NM that interface doesn't exist, and you'll get the behavior your see.
I hate to say this, but it become more and more obvious, that the ubuntu family is really a hopeless piece of sh*t. It is time to move on (or back to Debian).