Name Resolution

I have been fighting this problem for some time now and I hope someone can help. I have a network latency when I do a ping with a computer name (ping computer_name), but when I ping with an IP the response is immediate. I run an NT network. The latency when pinging with name is about 15 seconds and this can sometimes cause a problem with SQL databases. I have tried setting up a new WINS server, set LMHOSTS file and nothing seems to help. Does anyone have any ideas?

Thanks