the new WD drives are a little slower to initialize. So if you have a forwarder channel, it might not wake up the first time u launch it, but when u launch it the second time it should already be initialized (from your previous attempt) and work fine.
I recommend the Seagate GoFlex drives, they're the same price as the WDs or cheaper, they're faster to initialize, great compatability with the Wii (and PS3), and they're upgradable if you ever decide you want to switch back and forth between USB2.0/esata/firewire/USB3.0