Easiest way is just to add the second drive as a slave.
Leaving the other as the main drive, you can then move your documents pictures etc. to the new drive and leave the operating system and programs on the old drive.
if you really want the new drive as the master with the operating system on and you do not have XP to reinstall from a CD then you need to "clone" the old drive to the new drive. click here
once cloning is complete and you have checked everything works ok you can the wipe the old drive and use it as extra storage.