Yes, it's possible. Once you are done with one XP install, just put the disk in again and start the install process all over again. Just make sure you choose to do it on the other hard drive, and not to over write your other XP install. Next time you boot you can then select which install to boot too. You may want to make it easier for yourself so you know which partition is which. You can edit what the boot loader says by Right clicking on "My Computer" --> Select Properties --> Selecting Advanced" Tab --> Press the "Setting" Button on startup and Recovery --> Clickg the "Edit" button. The information in the Quotes is what the bootloader displays to the user.