Microsoft.com has posted a nifty grid at https://www.microsoft.com/windowsserver2008/en/us/compare-features.aspx that shows you which versions of Windows Server 2008 are required for the new features:

New and Updated Features in Windows Server 2008

KEY:

= Not Available

= Available

New/Updated Features

Enterprise

Datacenter

Standard

Web

Itanium

License Requirements

Internet Information Services 7.0

Available
Available
Available
Available
Available

Covered by server license. No incremental licensing requirements.

Hyper-V

Available
Available
Available
Not Available
Not Available

Covered by server license. No incremental licensing requirements.

Network Access Protection

Available
Available
Available
Not Available
Not Available

Covered by server license. No incremental licensing requirements.

AD Rights Management Services (RMS)

Available
Available
Available
Not Available
Not Available

Covered by server license, but incremental RMS CALs required, similar to Terminal Services.

Terminal Services Gateway and RemoteApp

Available
Available
Available
Not Available
Not Available

Covered by server license, but incremental TS CALs required, similar to AD Rights Management Services.

Server Manager

Available
Available
Available
Available
Available

Covered by server license. No incremental licensing requirements.

Windows Deployment Services

Available
Available
Available
Not Available
Not Available

Covered by server license. No incremental licensing requirements.

Server Core

Available
Available
Available
Available
Not Available

Covered by server license. No incremental licensing requirements.