this is a quick & dirty method:

dd the arch install image (a bootable cd image that doubles as a bootable hard
drive image) onto the hard drive.

edit partition table to add two more partitions:
- one big enough to contain a second copy of the arch iso
- the other one taking up the rest of the space

dd the arch install image again, this time onto the second partition (i.e. the
first of the extra two created in previous step)

(possibly optional) edit the beginning of the hard drive to blank out
occurrences of the disk label