I have a couple of these - your old hard disk should be SATA and this works with just a usb lead, no external power required:
Extra Value USB2.0 Caddy for upto 2.5" 500GB SATA.. | Ebuyer.com
Pop the old hard disk in it, then you can either migrate things or just copy them across to the new machine. Once you have retrieved everything you want, you will have a handy external hard drive.