Bad IP addresses in DHCP

keep getting bad IP addresses in DHCP. Microsoft say service pack should resolve this but this isn’t the case for us. can any one help? We have a server running windows 2000. We only started one or teo bad IPs last week now we are getting about 30 or 40 a day. We haven’t loaded any software on the server, but the server crashed last week and it seems that the problem started then.