Win2k server

i got a Win2k server with 2 NIC.
first one is with ip 192.168.0.1
Second one is 192.168.0.2
When i enable the second one, the message pop out ” duplicate name on the network”..why??

Another problem is after i enable this 2 nic…my workstationWin2k prof..log on very very slow..
its it because of the dns??