In addition to that Joudi, did you know that if you only have XP without SP1 that XP cant "see" more than 137 gig.
So if you have an original non SP1 XP cd and install to a new 160, 200 or 250 gig drive, it will only see the drive as 137 gig.
In this situation you have to create a partition to install XP onto which is smaller than 137 gig and then when you install SP1 or SP2 you can format the remainder of the drive as its full size