I found this interesting information while reading about Vista SP1 at Computer world. So it explains that Vista SP1 and Windows 2008 goes hand in hand, with a little help from XP SP3.
Interestingly, the initial, release-to-manufacturing version of Windows Server 2008 is known internally within Microsoft as the Service Pack 1 version. This is because both Windows client and server are now based on the same code, and have the same kernel. Along with this parity, the same patches and updates apply to both Vista SP1 and Windows Server 2008. It may seem strange to have the first release of an OS call itself Service Pack 1, but the first service pack for Windows Server 2008 will indeed be named Service Pack 2, and should appear in the channels at roughly the same time as Vista Service Pack 2.
Some other miscellaneous improvements relating to SP1 with regard to Windows Server 2008:
- Bitlocker, the drive encryption feature, now supports encrypting other volumes besides just the main C:/ drive in a system. The Bitlocker code in the Vista client has now achieved feature parity with that in Windows Server 2008.
- Terminal Services printing is improved, specifically when printing to a printer local to a machine from within a Terminal Services session.