Once you have installed the old HDD in your new computer and transferred all the files you wish to save, you could then delete the Windows XP partiton and create a new one just for backup, for things like system images. I like to save system images to the second drive in my PC, as well as to an external drive as a safety precaution. I had a storage HDD fail me without much of a warning two years ago and since then, I always make multiple backups of all my data on multiple drives.