There really is no need to use that old HD unless you've got some important files on it as it is very small and likely not very fast.
I'ld recommend to repation your current HD if you want more drives to save various files to. The downside to that means that you will need to format your current HD.
If the jumpercap (the thing on the back

) fits on your HD you can use it.
Where you should place might depend on the model, so could you write the model number from your disc.
Usually Maxtor doesn't require a jumber when used as slave. And you should set it as slave