DNS – hello123.com on LAN shows nothing

Domain name www.hello123.com (fictitious)shows webpage outside the company and mail.hello123.com retrieves POP mail.
Company’s W2K Domain name is hello123.com and smb hello123
On the Lan PCs, a hello123.com in IE show nothing and mail.hello123.com won’t retrieve POP email.
How can I chance the DC’s DNS , so that the main DC is not looking at itself for hello123.com but on the internet.
??
Please include steps or a URL/link to the all explaining white paper/Article