Since you are OEM:
Original Equipment Manufacturers (OEM) Customers
Customers who obtained their Windows Server license from a server manufacturer or installer (OEM) have the same rights to run a prior version or lower edition of Windows Server as Volume License and Retail customers: Customers may run an instance of an earlier version of Windows Server in place of Windows Server 2008 R2 or Windows Server 2008. However, the server manufacturer or installer are not obligated to supply and may not support earlier versions of the software. In addition, for some products, the OEM may not have any additional rights to supply the downgrade media.
You need to call the manufacturer to get the 2003 CDs if you purchased a server with 2008. Also, the supplier is not obligated to give you a 2003 CD set.
