Why in hell you want to go 50 pin connector to IDE to USB when one of the cheap case on ebay (around $17) have a PCB that goes 50 pin to USB already?
Just to clear all you questions (in case you didn't read my first post)
Do not use a IDE adapter go with the enclosure (usb from ebay or firewire/usb from mp3car)
Thanatos.
Edit:
pics
here is the connector that comes with the enclosure
front view:
Back view:
Enclosure front:
In this last pic you see the PCB in two parts, that is becouse the working one is in the car and this got burned