WD products have a sketchy history of compatibility with Macs. The MyBook can be partitioned and formatted for the Mac and will work with Time Machine, however, it cannot be used to boot the Mac. Most WD packaged drive systems simply won't boot a Mac.
Personally I'd suggest getting a drive system from MacSales.com and steering clear of WD. You can purchase a hard drive separately and an enclosure separately and install the drive yourself in five minutes. See the following:
Visit
The XLab FAQs and read the FAQ on backup and restore. Also read
How to Back Up and Restore Your Files.
Although you can buy a complete FireWire or USB drive system, you can also put one together if you are so inclined. It's relatively easy and only requires a Phillips head screwdriver (typically.) You can purchase hard drives separately. This gives you an opportunity to shop for the best prices on a hard drive of your choice. Reliable brands include Seagate, Hitachi, Toshiba, and Fujitsu. You can find reviews and benchmarks on many drives at
Storage Review.
Enclosures for FireWire and USB are readily available. You can find only FireWire enclosures, only USB enclosures, and enclosures that feature multiple ports. I would stress getting enclosures that use the Oxford chipsets (911, 921, 922, for example.) You can find enclosures at places such as;
Cool Drives
OWC
WiebeTech
Firewire Direct
California Drives
NewEgg
All you need do is remove a case cover, mount the hard drive in the enclosure and connect the cables, the n re-attach the case cover. Usually the only tool required is a small or medium Phillips screwdriver.
If your computer supports Firewire that would be my recommendation for speed.