OSX and DHCP server?

[R.L. Grigg]

I'm trying to connect an ethernet-enabled device to a OSX Macbook w/ 
RJ45 cable. and the device spec says it will configure itself if  
there's a DHCP server on the LAN, shouldn't this work? The device (a  
temp sensor) doesn't appear on nmap scans and I cant locate it on the  
LAN even tho the device is powered up and connected to the ethernet  
port of the Macbook, and the Network utility shows the en0 link  
status is Active and gives a IP address. Airport is off. Is there a  
setting on the Macbook to make this work or do I have to install OSX  
server?
Russ