My understanding is that any usb drive that is plugged onto the 360 must be fat32. Are you saying you have tried other usb's formatted with HFS+ at they work? I just did a quick google of HFS+ so I dont know much about it but if that is the case, I would bet you did run into some size limitation.
Hopefully that knows more about this format posts.
Let us know if you find a solution.
QUOTE(Patrick33 @ May 13 2008, 05:20 PM)

I recently got a 2TB Mybook premium edition II to put my few 500 gig encolsures worth of wmvhds on, and I formatted it to HFS+, then placed all of the data on it. However, when I connected it to the 360 it does not show up, yet my others do. It doesnt even show up when it is the only drive connected. Is it because the drive is too big? Are there size limitations? or is it because it is an enclosure that has (2) 1TB drives in it? Thanks in advance.