Actually, might be there were some reasons to add an alias for Windows 2003 AD. Though u did not mention here what is the purpose ! Often it is also called as CNAME
Hope, u properly created a cname / alias…..
1. Navigate to DNS thru administrative tools
2. Here, click the + and expand the host name
3. Again try to expand forward lookup zones
4. From here, right-click the lookup zone (what u want & then click new alias
5. On next box (i.e. alias name box) just type www with FQDN of the DNS server