I am using an iMac with a WD My Book as external boot. But since I up- graded the OS to 10.6 the screen locks up,I can move the cursor with the mouse but clicking on anything does nothing. If I switch and boot from the Internal Mac HD this doesn’t happen, if the My Book is even plugged in, but I am not using the software on it the screen will lock up again,could it be that I need to install 64-bit firmware? And to download firmware updates will Fire Wire work instead of USB?
Be sure that you have the latest firmware update, also you need to have it connected with the USB cable to update the firmware.
There is not 32 -bit or 64-bit firmware. Check if this information helps you to sort out your issue: List of Mac-bootable WD external drives and how to format them to install on operation system
You may also test the drive in another computer, in order to compare results.