this is a mac question

i have an iMac connected to our NT server and we are using DHCP. All other imacs in the same room are getting the appropriate IP addresses and subnets. This one machine, is getting an address of 169.n.n.n with a subnet of 255.255.0.0 (the correct is192.168.n.n with a 255.255.255.0)

I cannot delete this particular setting. Any ideas to get this machine to work correctly?

Apparently, this machine worked correctly a few weeks ago, but has sinced began acting in a strange fashion…

Any thoughts would be helpful (and no, get rid of it and replace it with a PC is not an option!)