good drive. just keep the old one.....well, how old is it?
that's the variable that determines alot of things. if its pretty old, you may want to consider transferring your data to a new drive. how? you have to use some sort of disk imaging program....but that is beyond my range of current knowledge.
i say its a good idea to have windows and programs on your oldest or least reliable drive just because if that drive crashes you can always reinstall windows and other programs. if all your data such as pictures, music, documents were on the old drive, then if it crashed it would be hard if not impossible to get that data back.
hopefully someone else will chime in give you more details