In case your server is connected to a network which broadcasts DHCP you didn't get a chance to configure a static IP address for your server.
ifconfig and copy the output somewhere so you have access to network information you got from a DHCP server.
Open up /etc/network/interfaces with nano and replace
auto eth0 iface eth0 inet dhcp
iface eth0 inet static address YOUR-IP netmask YOUR-NETMASK network YOUR-NETWORK broadcast YOUR-BROADCAST gateway YOUR-GATEWAY # dns-* options are implemented by the resolvconf package, if installed dns-nameservers YOUR-DNS-SERVERS-SEPARATED-BY-SPACE dns-search YOUR-DOMAIN
Reboot your server, check that your internet connection is working (try to ping google.com or some other host) and if everything is ok you can remove dhcp3-* packages from your system.
apt-get --purge remove dhcp3-common dhcp3-client
Note that option –purge removes configuration files of the packages we are removing. If you do not use –purge they will be left on your system.