Can I move my Operating system on my old Hard drive to my new Hard Drive?
not if you do it right, make the 640 a slave drive (jumper on back of drive), copy all you stuff onto 640, after a format, use a cloning program, or if you have backup disc copy to 640, once that is done, make 640 master (jumper on rear and BIOS) and pull out old or reformat other, other way is to modify boot.ini file so you can install OS on 640 drive, then you have option as to which drive you boot up to, once you moved all over change boot.ini back to normal, make 640 master and do what you like with other. So it will work just remember to chang jumpers on back of hard drives.
You will have to redownload Vista from your original CD as the old drive’s registry keys won’t work on the new drive. You can transfer all your files, documents, pictures and games but many games won’t work on the new drive either unless you re register them, again the registry keys are different for new hardware. been there.