Hello,
I’m having a Mac-Formatted USB-Disk attached to my WDTV too and never had any problems with that.
But, some external drives have a problem to power up while sitting only on USB. You should try either a diffrent cable (preferred a short one) or interface on the WD.
Also, if your LaCIE supports a external power source you may also try these.
Hope that will help you.
Lupunus