After Install LAMP Server Locally on Ubuntu 9.10(Karmic), I have to change to a static IP address because Ubuntu installer has configured my system network settings via DHCP. Edit /etc/network/interfaces as follows for example,

$ sudo nano /etc/network/interfaces

(nano is a simple terminal based editor, very easy to use)

# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.1.2
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
gateway 192.168.1.1

then restart the network services,

$ sudo /etc/init.d/networking restart

Setup manually DNS servers in resolv.conf file when you are not using DHCP.

$ sudo nano /etc/resolv.conf

#search domain.com
nameserver 8.8.8.8
nameserver 8.8.4.4

By the way, 8.8.8.8 & 8.8.4.4 are the Google Public DNS Service IPs, you can use the DNS IPs at your choice, of cause.