booting from a Windows Vista drive that used to be C drive but now in a USB case

Question

Hi I have upgraded my laptop with a solid state drive and Windows 7.

I still have the old Vista install on the old hard drive.

I would like to be able to boot up from the old hard drive without having to swap out the two hard drives in the laptop.

I have put it in a usb case and selected it as the boot drive. When I start the system it tries to boot from the Vista USB but then gives a BSOD.

Is this possible? and if so is there anything I need to do to make it work.

Thanks,

Henry