are for mapping a win drive to believe it's on hda if you decide to place it on hdb for some reason. So maybe at some point in drive transitions it became necessary to have those lines; however since XP is now on hda you no longer need them and commenting them out should work.
hdd1: I see the confusion. In linux hda and hdd are 2 different drive locations. hdd1 to you means your first hdd, where to a linux user this means the Secondary Slave drive.