Removing casing of a laptop hard drive

[Xtremepenguin]

I have bought a 20gb hitachi laptop hardrive for a photo backup bank. But for some reason there is an extra bit of casing underneath the drive, that doesnt seem to serve a purpose and wasnt in the picture on the ebay auction. this bit of casing is stopping the hard drive fitting into the case its going into.

It looks like it screws off but i cant unscrew the screws.

http://www.bobcatterson.f2s.com/hardrive1.JPG


any ideas?