Are you getting the error "The system is not fully installed" after you've resealed?
It's a known issue with Media Player 11 and pre-installing & certainly one I've experienced first-hand. Oficially Microsoft still don't support deploying WMP11 in a corporate environment

but they did release a hotfix with an updated version of Sysprep which supposedly fixes the issue...
BUT I managed to get hold of the hotfix and did a test install of my custom XP image (1.4Gb DVD - only 3 items on Windows Update after install, 2 of which are IE7 and WMP11

) & resealed with the new version of Sysprep with no change - still got the error on restart. Not a lot you can do at the moment I'm afraid except provide a link to install it manually once XP's been deployed
More info:
http://support.microsoft.com/?kbid=925507
http://www.kbalertz.com/925507/Wind...g.incorrect.version.Windows.Media.Player.aspx