I am confused to what you have done , you say you have cloned the HDD , what have you cloned it to ? another HDD or an image ? both can be done .
You then say you installed XP and the clone will not boot , which HDD have you installed XP? the cloned HDD? do you mean you have reformatted the original ?
Normally a cloned HDD would be swapped over with the original say if the original died , or if the original became corrupted , you could replace it from a cloned image or drive .
Can you be more specific to what you have done .