If I don't have any external drives, can I still create a full system image? Can I create a separate partition, and image only the original partition, to be stored on the second partition? Or does it need to image the entire drive?
It would really depend upon the amount of remaining disk space you have and the software you are using. Some imaging programs will image data+free space. Others won't. I would tentatively say you can make a disk image to another partition on the same hard drive, if the imaging software supports it. If you plan on keeping the image on the separate partition as a backup, be advised that should the hard drive go you will potentially lose both your system and your backup.