Vista Possible DNS Problems

Having a bit of a problem and would appreciate anyones help. Here's a quick
breakdown.

Vista Business (with all updates and service packs as of 7/11/2008)
One a Class A Network
Domain Controller, DHCP, DNS hosted on Server 2000 & Server 2003

My client can bring up local intranet pages fast as ever, but when you try
to venture outside of intranet and go to web pages like yahoo, mypsace,
etc....very very slow and sometimes doesn't completely load the page. Any
ideas anyone ?