I do have the Guest account. I have been going into each other user account and saving what I want from those accounts to my new Mac account and then deleting things on those PC accounts as I go. I hope this works. I did notice that my iTunes music is not all there for some reason, almost as if it transferred music from a library almost 5 years ago.
I haven't used a Windows machine since 1995, so I'm on somewhat shaky ground here.
If Migration Assistant will allow you to select what you want to transfer, try moving your iTunes library over (I have no idea where it would be located - see above)
If your can 'see' the PC in the Finder sidebar (you may have to enable Sharing in System Preferences), maybe you can copy the library over and import it. Hopefully you won't end up with double entries, but at least you would have all your music.