Windows XP Service Pack 2 offers users many changes which greatly enhance the security of their systems. What it also does is install the Service Pack 2 build of Media Center on to any existing (Non Beta) version of Windows XP Media Center 2002 or 2004 installation. So if you've not yet been able to obtain a Media Center 2004 upgrade from your OEM, SP2 can help here.  This update doesn't provide any new features that were not included in the last release (MCE 2004 with Q830786 installed), this is mainly a bug fix. The current build number for this build is 5.1.2600.2096

NOTE:  The current version of Service Pack 2 is a Release Candidate.  It is still Beta software, and may cause unforeseen problems on your system. The final version should be with us Summer 2004.

Download:
http://www.microsoft.com/technet/prodtechnol/winxppro/sp2preview.mspx