Win 7 does not recognise external HD (caddy)

Hi all

I bought a laptop hard drive 2.5" 160gb Samsung and also a cheap external caddy for it from ebuyer.

I'm trying to connect it to my laptop via usb so I can install xp onto it for a friend of mine, his laptop hd has died and theres no dvd drive for some reason. however when connecting it to my laptop via usb my laptop installs the drivers automatically and even gives out a noise when I plug it in and out but the drive does not show up in the "my computer" window. I also tried it on a computer at work.

I thought the caddy might be faulty so I tried it with another (i bought two) but that gives the same result.

any ideas why my laptop and a work computer can't register the hard drive?

thanks!