WD My Book Firewire Not Reading

Picked up a WD 320GB Firewire capable external HD at Best Buy today on sale, yet after I setup, not reading firewire. Tried to see if it would read USB and it does, but no firewire read. Before I pack this thing back up and return it, any ideas out there? I'm using an intel based iMac and all software updates are current, looked through WD website for support, nothing. Not the end of the world if it doesn't work, but don't have a lot of money to spend at this time on adding more space.

Thanks in advance for any feedback....