A mac won't start in target disk mode on an XP machine. There are several options.
You can set up windows sharing on your mac and share your home folder with windows.
You can use an external FAT32 formated drive to just copy the iTunes music folder from your home folder, and then copy the iTunes folder to the pc.
You can make a data DVD of your music, and then put it into the XP pc.
Whatever method you use to get the iTunes music folder onto the PC, all you have to do is start iTunes on the PC and tell it to look for your music in that folder. It'll make its own new library with the music found in that folder.