AlanC, The cassette that came on your bike will work as before. To go to a larger cassette the number on the cassette will tell if you can go to a larger gear. Get the number on the cassette body and check with your LBS and they can tell you if a 12-36 will fit. Most of the time on an older bikr you also have to change the derailleur too because they match 'em to the cassette and the biggest used back in 2002 was a 34. The larger 36 cassettes come on the new 29ers and full suspension bikes to off set the weight. To answer your question go back with a 34 and you'll be fine.
Fat Billy sponsored by: Any all you can eat buffett, Michelin, Panaracer, Shimano, Serotta Bicycles, Sidi shoes, Bell Helmets, Monkey light Handlebars, Camel Back products. Wait a minute I give them money and all they give me is high prices. Never mind! Too wet to ride? Try Planking to help keep muscle tone.