I am installing DHCP on my internal interface eth0. I have setup dchp.conf and started the service. Because I have no machines connected to my LAN right now I want to check that it is working.

I edited the DHCPCDARGS paramter in the networkconfiguration file so it read

DHCPCDARGS="-d" I was led to belive that this would force the ifup script to log debug code in /var/log/messages.

When I add the "-d" and restart the DHCP service it doesnt come back up.

Does anyone know whats wrong here, or another way I can check that this is working correctly.

That debug mode is to be used from a terminal so you can watch the output...
The usual log output goes to /var/log/messages..