Upgrading XP Pro to Media Center Edition

[justacruzr2]

Does anyone know if there's an upgrade version of MCE 2005 out there?  I have a version of MCE 2005 that I tried to use to upgrade my XP Pro but it didn't offer the option to upgrade.  I was doing this the normal way by putting in the install disk and then rebooting the computer which takes you into the blue screen setup.  I also tried it by putting the disk in after I had already booted into XP and then clicking on Setup in the root folder of the MCE 2005 disk and selecting install Windows XP from the Welcome to Setup screen.  The first message I got was "The option to upgrade will not be available at this time because Setup was unable to load the file F:\WINNTUPG\NETUPGRD.DLL" (F: is the name of the CD drive the disk was in).  I looked at the folders on the disk and yep, there wasn't any folder named \WINNTUPG.  When I was doing it the normal way and got to the agree to the EULA screen, I scrolled down to the bottom where I got a valuable piece of information.  Don't know if this is the version number of the disk or the EULA but here it is:  MCE_05_RTM_OEM_EN.  I'm assuming that the "OEM" part means it's the OEM version and I suppose that the upgrade option wasn't offered on that version since the OEM wouldn't be upgrading, they would be doing fresh installs.  So is there a retail version available for downloading out there?  I want to upgrade my XP Pro SP3 version to MCE without losing any of my apps or their registry entries.  And will I need to temporarily remove SP3 in order to upgrade?