Just quick config snippet for Debian 6.0 which I came across when setting up few Debian Linux 6.0 virtual machines for recent network LAB. By default network adapter is set to get IP address from DHCP.

/etc/network/interfaces – dynamic IP address configuration

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface auto lo iface lo inet loopback
# The primary network interface allow-hotplug
eth0 iface eth0 inet dhcp