A laptop image will have all the wrong hardware drivers for a desktop and vice versa.
On top of that many OEM versions of Windows are keyed to the OEM's equipment.
Not knowing what you mean by: 'Windows on my Desktop PC is a bit stuffed.' it is bit difficult to help further.
However if you are suffering from performance problems, that question has been asked and answered many times and so I suggest a quick search of all the answers here.
T
February 2009
howtomendit.com for free repair help, information and advice.
