Archbootstrap-ee is a small script to bootstrap an Arch Linux installation from a running Arch Linux. You can download it from the AUR (present as AUR).
archbootstrap-ee <architecture> <targetdirectory> [mirror] [pkgcache]
architecture and targetdirectory are needed paramteres. Architecture can either be i686 or x86_64. Target directory can be any directory, it will be created by archbootstrap-ee.
By default, archbootstrap-ee uses ftp.archlinux.org to retrieve the needed packages. You can change it to any other, but you have to escape it.
would turn into
$TARCH will be set by archbootstrap-ee, $repo is used by pacman.
The archbootstrap-ee package will create an additional directory containing the cached packages. If you are on x86_64, /var/cache/pacman/pkg32 will be created and vice versa. You can change the cache to any directory.