What prompted you to buy a 3rd party disk defrag program ?
Do you know that your Vista has a built-in defrag program that does the job
amicably in the background almost constantly ?
You don't need to buy one, but if you must ( in order to be trendy ), DO NOT
buy program that does Registry Defrag.
DISK defrag and REGISTRY defrag are 2 different things. The former is ok to
use, the latter should be avoided at all cost.