I personally needed a to get a fellow user's PC into German, and we wound up using an "anytime upgrade" to ultimate and then the MUI from Microsoft update. (This was in an SMB environment.)
MSDN Has a learning section totally devoted to MultiLingual User interfaces
You can access this information from searching for "MUI" from the MSDN.Microsoft.com Homepage or via this Direct Link:
From their site:
There are two main categories of language packs:
complete language packs
Language Interface Packs (LIPs)
Both complete language packs and LIPs are used to localize Windows UI, and both are built using the same underlying technology. However, there are significant differences between them, mostly related to the localization coverage they provide for the system user interface and the licensing rules that apply to them.
Ultimate Edition (and enterprise) users can download and install language packs from the Microsoft Windows Update site .
MSDN subscribers can download language packs from MSDN download center .
Registered OEMs can obtain the language packs as part of an OEM kit.
Enterprises can obtain language packs through their Microsoft Volume Licensing agreements .
Server language pack can be obtained from the Microsoft Download Center.
LIPs can be downloaded from the Microsoft.com download center .
OEMs and System Builders can download the LIPs from the OEM partner site and pre-install them or redistribute them on media.
For more information, see Local Language Program
Language Packs in Windows 7
Language packs contain the resources required to translate all or parts of the user interface (UI) of a Windows operating system into a specific language.
Language packs existed prior to Windows Vista, but they could only be applied on top of a specific language edition of Windows, typically English.
With Windows Vista and Windows 7, the multilingual user interface (MUI) technology is core to how Windows is built. In Windows XP and earlier Windows releases, UI resources were packaged together with the code binaries to build language-specific versions of the operating system. Now, UI resources are separated from the code binaries and packaged in language packs for all languages—including English. In Windows Vista and Windows 7, using this mechanism, language-specific versions of the operating system are built by assembling the language-neutral code binaries with a language pack that delivers the operating system UI in the desired language.