http://www.macally.com/spec/usb/stor.../phr_250a.html
+
http://www.westerndigital.com/en/pro...mp;Language=en
it will cost more than a 3.5" desktop drive, but the enclosure is TINY and the device powers itself over usb. both are available at newegg.
the macally enclosure is good and only needs 2 screws for installation. western digital is one of the few vendors that provides windows-based diagnostics software, so you can scan the drive properly if it begins to act up (good luck with dos+usb otherwise).