Just like most of the Windows Operating systems come in different versions for different purposes depending on what the customer needs. Lets say small business to large corporations, the small business only needs a small portion on the software then it can be cheaper.
Versions of server 2008 1-Standard (just like the windows 7 starter version)A step up from the web server more features
2- Enterprise Very expensive and packed with features
3-Datacenter Super expensive with all the whistles Max CPUs at 64 !!
4-Server 2008 WEB Least Expensive not that many features
5-Itanium based for those CPUs architecture
New features for the 2008 server are many, is faster than 2003 with increased security.
Hyper V Virtualization and is more efficient than 2003. The installation process is more friendly with GUI searching is also better. The 64 Bit architecture are more powerful than the 32 ones it can access more ram than 32 bit and the bus is wider allowing it to access more information at a time. The new features like server core allows for a different installation of the services according to my research is not available on all versions on server 2008 but standard enterprise and the data center editions, this is a more simple way to install services with limited GUI and thru the command prompt. Another feature is Virtualization that is embedded on the operating system itself with no install required. This allows you to run multiple