Windows XP MCE - Emerald is a “Service Pack” like update to Symphony (MCE2005).
Designed to be installed on top of an existing installation of Symphony (Emerald.exe)
Microsoft will make this update available as a Windows Update Recommended download around 8/12/2005

Feature Overview
Emerald is a "Windows Update" to Symphony. Included Features are:

Native digital cable support;
Platform security
Always Ready (instant on)
TV enhancements
Dual ATSC tuner support
10' resolution switching
“Zoom Mode 4” (Non-Linear Zoom)
708 Captioning Support (US required by FCC)
Emergency Alert System Support (US)
Enhanced DVD Burning (Still requires separate licensing payments per Symphony ‘Digital Media Feature Pack CD')
New Locales and Languages- large international expansion
DVD changer support
Lowering remote control costs/complexity
Added suppliers and minimum stocking requirements
World Wide Iconized remote design option
Updated HW requirements
Reliability
MCE automatic optimization (nightly ehshell restarts to improve reliability)
Prevent 3rd party apps from hanging MCE

Installation

Windows Update Install
Windows Media Center Edition Update 2 will be available via Windows Update as a free download to existing Windows Media Center Edition 2005 customers. Microsoft® Windows Update is the online extension of Windows that helps you to keep your computer up-to-date. Use Windows Update to choose updates for your computer's operating system, software, and hardware. New content is added to the site regularly, so you can always get the most recent updates and fixes to protect your computer and keep it running smoothly.

Please visit http://update.microsoft.com/windowsupdate to install the update.