Rule #1. Do not use commercial oven cleaners in a microwave.
To remove spatters from the interior of your microwave experts recommend mixing 1 cup water with 1/4 cup vinegar in a glass container. Place inside the microwave and boil (about 3 minutes). Then you should easily be able to wipe away spatters and grease with a damp cloth.
Odors can be removed by pouring some vinegar in a dish and leaving to sit overnight in the microwave. If necessary, repeat until the odors are gone.
For information on replacing your old dirty microwave with a shiny new one, contact the friendly folks at Universal Appliance and Kitchen Center in Studio City.