If you think you can install your old hdd with the old OS into the new machine and get it to boot and run that's doubtful.
You could fit it into the new machine and install the old OS and the proper drivers and then use the bios to select which hdd you wanted to boot from.
My old pc died but the hard drive is fine. I bought a new PC with an hd expansion slot and proper connections. I'd like to install my old hd and operate TWO SEPARATE systems that don't communicate with each other. Can I do so? and if yes HOW??