|What do you mean by only working at 53%? Explain, 53% of what?|
If the XP Pro on the other hard disk was installed on another computer it will not work on any other unless the hardware of both computers is identical.
You would be better installing the second hard drive as backup device, copying the data you need and sorting out whatever the problem is with the Vista drive.
Whatever you do, if you want to use Windows XP you are going to need a Windows XP installation disk. Do you have one?