You might need to format it in XP but this is fairly easy, if you attach it like djwhite said then boot up XP should auto detect it, though until it is formatted it will not show up in "My Computer".
So you will need to goto Control Panel then Administrative Tools, and open the Computer Management interface.
Then click on Storage in the Computer management window, then Disk Management (local)
You should be able to see your new disk there as well as the old one.
Right Click on the New Disk and select Format.
I am not 100% sure what you can do after that as I dont want to accidentily format either my system drive or my data drive, but if you get that far and arent sure what to do then post a screen shot (press Print Screen button then open Paint Shop Pro or other graphics editor, then either press Ctrl+V or create a new image, then paste. Then you can crop the image down to the size of the format window)
I apologize if that last bit on screen shots was insulting I am just covering all the sections
I think you can also partition with the disk management tool, but your performance will be better without a partition according to dealer - another user here.