Yes it can be used as an external hdd.
This is the only procedure i know and i hope you'll be satisfied.
Things You'll Need
Locate and purchase an IDE to USB cable conversion kit. Insert the driver CD that came with the kit into your computer's CD drive. Follow the instructions on the installation prompt that will appear on your computer's screen to install the conversion cable driver software.
Power off the computer once the driver software has finished installing. Remove the power cable and all of the other cords from their ports on the back side of the computer.
Set the entire computer case on its side so that the left side panel is facing upwards. Check the back end of the case to determine if the side panel is locked with two case screws or only a metal latch. Disconnect the panel from the case either by removing the screws or by pulling upwards on the latch.
An IDE Cable
Pull the side panel off of the computer case and set it aside. Locate the drive that you want to connect with a USB cable. Remove the screws holding the drive into the drive bay. Disconnect one end of the IDE cable from the motherboard, but leave the other end connected to the back side of the drive itself.
Remove the drive from the drive bay with its connected IDE cable and set it outside of the computer case. Set the side panel back onto the case and re-attach the metal latch or case screws. Plug the cables back into the computer ports and power the computer back on.
Insert the end of the IDE cable that used to be connected to the motherboard into the IDE port on the conversion cable. Plug the male USB end at the other side of the conversion cable into any open USB port on your computer.
Have a nice day friend and i hope this would satisfy your needs.