control panel/administrative tools computermangaement
click on the disk managment on the left side, you can change everything from there
one other thing, are you wanting to boot from the new drive? if so, it's a little more complicated... yu need to either install XP on the new drive, or copy the contents of the original drive to the new one (cant jsut copy and paste, you'll need to format (erase everything) the new drive than copy the entire image of the smaller drive using the disk management)