In the FreeBSD section I offered a solution to backup over the network to your Apple box, so you could use the Apple HFS+ formatted external USB drive
Because I don't have neither an Apple (my old Apple II obviously doesn't count), nor an HFS+ formatted USB disk, I used OpenBSD as example.
Code:
# dump -0auf mnt/file.to.dump.to /dev/wd0a
Repeat for the other partitions/labels on wd0
Section 1.3 of
http://www.daemonforums.org/showthread.php?t=2232 tells how to mount the disk.