Know that problem? You are somewhere around and got special network settings like a wlan essid and static ip ressources. Your Gnome network manager which you really like as it finally brought easy wpa2/wpa/wep detection and setup to you prefers dhcp and skips around the networks like mad.
So this is the time to consider going back to the roots: Switch it off. Just disable the network manager by right clicking on it. Now open /etc/network/interfaces in an editor of your choice with sudo/root rights and add something like this:
iface mynetwork inet static
Fill this with your specific details and yes, just choose a name for the interface you like. Don’t edit an existing one, don’t think about connecting it to a real interface right now.
After you have done this, open a terminal and do something like:
$sudo ifdown eth1
$sudo ifup eth1=mynetwork
What you just did was to manually bring up the network interface with a hint which network profile from /etc/network/interfaces it should use. As you have disabled the network manager you should stick with the network now.
See “man interfaces” and “man wireless” for more details.