The drive that got put in their was formatted on my Macbook (replaced with a larger HD) using HFS+.

If I boot into Windows, MacDrive saw the drive just fine, OS X no go. Tried to reformat in OS X, but the drive does not even show up in Disk Utility. I have since tried formatting with FAT32 and NTFS under Windows and again OS X does not see the drive, even in Disk Utility. I have even deleted all the partitions and left it literally a blank drive with no file system. No matter what I do I get that same error message in OS X while Windows (and now tested under Linux) both see the drive and can play with it just fine.

Hey, Recks im sorry to post so late... but i may have the solution to your problem, i too had a problem with my external HD locking up, i was processing some music in iTunes and it suddenly stop, my hard disk was still flashing but it didnt function..

i searched around and ive came up with this solution.

Macs, are best to be used with Hard Disk Formatted in this way

HFS+ Mac OS Extended (Journaling) <the journaling can be optional when you formatted this way.. no worries with the speed penalty if you dont want journaling it can be turned off...

My hard disk is the Western Digital 320GB USB My Passport Essential 2.5 inch HDD

Soo after formating the problem still existed...
checked console for the problem and it seem like the process of trying to write files into the Hard Disk may have timed out...

I decided to go to Disk Utility in the Utilities folder, and i did a simple quick Verify and a Repair of the Disk, when doing this, both processes will show you that the Hard Disk was fine.... but after the fix... you'll realise you can write things without mess again...

well atleast alittle larger files, i copied stuff 1 by 1 for 1 GB didnt try to move the whole library to the HD, cuz i didnt want it to happen but before the repair, i cant even move 1GB, it freezes around 40mb, so im real please with the fix... not sure if its surely the case, but ill give it a try!

good luck!