Instead of creating a special HFS partition, one can run MacOnLinux using a file as metioned on the linuxppc-list [1].
e.g. a 500MB image for MacOS:
debian:~# dd if=/dev/zero of=/tmp/macos.img bs=1048576 count=500
500+0 records in
500+0 records out
524288000 bytes transferred in 60.964236 seconds (8599927 bytes/sec)
500+0 records in
500+0 records out
524288000 bytes transferred in 60.964236 seconds (8599927 bytes/sec)
[1] http://lists.linuxppc.org/mol-general/200008/msg00014.html