Why isn't my DHCP release working?

I keep on getting conflicting IP addresses whenever my mac reboots and I have another machine on the network. For some reason, even though the network is set to DHCP it is always trying to use the same IP address 192.168.0.101, even if it's in use by another machine on the network.

So I go into advanced settings and click the Renew DHCP button but nothing happens, no IP address or anything. I have to reboot the mac in order to get another IP. This is on Snow Leopard.

Any idea what could be causing this?

Thanks.

Try rebooting the router doing the DHCP?

Rebooting the router works. But I shouldn't have to do that every time should I?

No you shouldn't. I was just wondering if it was the router that was screwed up and not the machine.