is it possigle to block site from DNS Server windows 2003

I want to block website like youtube,ibibo for my client computer in dns server of win2003 how do i do that ?? i know to that i can be done by makeing entry in host file of c:\windows\..\drivers\etc but that i have to followon all computer but i want to do it from server

we have DHCP network with WIN 2003 serer and XP on client machines

If anthing done from AD that also can do??

Pls help