Q: how do i sync all my music from windows media player with itunes?

You'll have to add the music to your iTunes library by choosing this option from the menu in iTunes-> add to library, and point iTunes to the folder where the music files are stored on your computer.

Use MusicBridge. I'm using it since years ago. https://sites.google.com/site/jrmwillis/

Four years on and it is possible the original poster is no longer looking for a solution. Since the topic has come up however I'll also offer my suggestions in Getting iTunes & Windows Media Player to play nicely. WMP 12 handles AAC natively. As long as you make metadata changes in iTunes WMP should pick up on them.

tt2