Let me ask a different question. How did you configure that interface? Have a look under (I think) /etc/network. There is probably a file "eth0" or something like that. What's in it? What kind of network hardware do you have? If it's PCMCIA, is the PCMCIA system running?
DHCP - this is where computers ask another computer for their IP address, gateway, DNS servers, etc., rather than being manually configured.