virtualbox - Setup static Ip in virtual box

I have as issue i am Ubuntu desktop and i have installed virtual-box(4.1)
ISSUE:-
Ubuntu 11.10 desktop is my host operating system and on Virtual-box i installed Ubuntu server selecting bridge adapter as my first adapter by default my network interfaces file get ip address by dhcp server but i want to setup an static ip.

by changing network interface file to static and gave some static ips my internet stop working on guest operating system(virtual-box -> Ubuntu server).

Can any one help me how can i setup static on virtual-box so that my internet will work too on my guest operating system.

thanks in advance.