I tried to convert my mp3s to AAC. And in "Tools" -> "Folder option" -> "View", uncheck "hide extension". Then you can see and change the extension here from .m4a to .m4b. As I know .m4b can enable the bookmark. (not so sure)

"Malcolm Adam's Applescript" is not for PC users.
Let me know if you have any trouble. By the way, all the musics are in the hidden folder in ipod. So just check "show hidden folder" and you can copy them out of ipod. Again, I use winxp.
Billy