The hard drives inside a WD My Book World Edition use the EXT3 File System, which is not supported by Microsoft Windows. You will need a specialized application able to read EXT3 partitions in a Windows environment, or a Linux-based system.
Careful using the windows based ext extensions, they have been known to mess the drive up pretty bad. Not physically, but the data on it rather. I cannot usually get them to work very well.
I would agree with Trancer as far as using a linux environment to read the drive. I might suggest booting from a Linux Live CD/DVD. Most mount the drive by default and can just read them from a file exporer.