connect the two Macs with a firewire cable, boot the
source Mac in
Target Disk Mode and drag the
entire iTunes folder (not just the iTunes
music folder) from <MacintoshHD>/users/<yourname>/music on the
source to <MacintoshHD>/users/<yourname>/music on the
target,
replacing the iTunes folder in place there.
these reads will be helpful:
one and
two.
another, more recent, article
here.