FYI, quite a few people have had problems trying to use WD MyBook & MyBook Pros on Macs. You can search this forum and find the threads.
I suggest you look at Lacie, G-Technology, Granite Digital, or OWC units. A very nice choice would be an
OWC Mercury Elite FW enclosure with a
Seagate 7200.10 drive in it, that is, if you're willing to assemble it (not hard at all, as long as you can use a screwdriver) <grin>.