Not the same. MCE 2005 is classified as a home OS and therefore does not have the ability to join a domain like XP Pro. However, disk 1 of MCE 2005 is a normal XP Pro cd. The MCE product key makes the installer call for cd2 which then makes it MCE 2005.
I installed MCE2005 using a normal XP Pro SP2 disk and cd2 of MCE 2005 a few days ago. Works perfectly with only one difference: there is no MCE visual style. Just the normal XP type. Do you know of any other differences between the 2 disks?
I experimented with upgrading WMP in MCE a couple of years back and the only hiccup was auto playlists was gone. Auto playlists was cool because it remembered your music choices based on time of day etc. and made playlists accordingly. I then rolled it back to he previous version.
MCE 2003 used same CD1, later versions are different. TabletPC uses exact same CD as Pro for all versions