you can add ringtone by when you have your phone plug into you pc. Pull up windows explorers with in one of the files you will see Ringtones. Just drag and drop your ringtones into that folder.
Once that is done go to the person that you want that speacial ringtone for edit their profile on the phone and scroll down within that profile right below they home phone number you will see custom ring tone.
hope that helps to do your own ring tones go to: http://phonezoo.com you can create your own ringtone from a song you like and the best part it's FREE