dchp and ip static

[minis]

hello everybody i am new to linux. I want to change my isp dns overwriting them with openDNS. I wan to use only them, deleting the first one. Can you tell me how to do this on ubuntu?
I have another problem too. I don't know if to be able to set open dns i must have a static ip. I am connected trought a 3g usb modem, so I don't know how to configure a static ip in this case. Do i have the dchp if i am behinde a 3g modem?

 

[RussG]

if you are using a 3g then you can't enter a static up or change the dhcp without Breaking your connection.
if you had an adsl Home like you would be able to do all you desire.