There may be a boot image that will allow you to boot from your usb hard drive. If you can use the external usb CDROM, look for a README or similar file for information. I used to have an HP laptop where my internal CDROM went out, and installed Mandrake linux from a usb CDROM drive.
If you did copy the cd image to C: then /dev/hda1 is where the image is located.
By the way, an image is a copy of the entire cdrom, and usually is given an .ISO extension. It will be a large file, about 650-700 Mbytes. Don't be offended, for pointing out something you probably already know. Sometimes people will do something like simply burn a CDROM file with an ISO file in it, rather than using the image to burn a disk.