Clarify: does that host exist in your local trusted network, or are you trying to ping it (an outside host) from within your trusted network?
If the host is in your network, then you are probably finding yourself trying to access an internal host using an external address, which doesn't usually work. You would need to create an internal record for it in your internal DNS.
Assuming it's on the outside, have your tried pinging from multiple hosts in your trusted network? Just to rule out a host having something in a hosts file.
More on that angle: when you run NSLOOKUP, are you pointing at your local DNS server? Or is it pointing at an outside server. If you point at your local DNS server (internal) and it resolves properly, then I don't think it is your DNS server that's giving you the loopback address as a result. I think that's more likely to be coming from the local host.
On a host, do an 'ipconfig /flushdns' and then do a 'ipconfig /displaydns' to show what's permanent in the local cache.
ShackDaddy