The adaptor you need is the *opposite* of what most people are looking for - most people want to connect their 2.5" drive to their 3.5" drive cable, but you are looking to connect a 3.5" drive to a 2.5" cable.

This seems to be what you require, but best to check first (and shop around a bit more!):

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3436287534&category=41993

Gareth