Measure the floor space in your kitchen. Then determine how much space you will need for moving around and cooking. Bear in mind that you will probably be bending over or kneeling to retrieve things from lower storage. You should also open any cabinet and appliance doors (refrigerator and dishwasher, for example) to make sure the new island will not interfere with your ability to access your food and dishes.
Measure your cabinet. Be sure the width and length will work for your space. Again, your china cabinet should be no taller than your counters. Many china cabinets have glass storage above wooden drawers and shelves. This top section can be removed for moving purposes.
After emptying the cabinet, check carefully for signs of wood glue. If the upper portion is attached only through brackets and screws, disassemble the cabinet to isolate the lower half. Carefully lift the top portion to be used individually or given away. Don't worry if the top surface of the lower half is missing or damaged; you can always add a counter-top later.
Paint or stain the cabinet. If you want the island to look like it is an original part of the kitchen, match the color of the cabinets as closely as possible. This may mean using a dark wood stain or a few coats of paint. Remove any knobs or drawer pulls before applying paint to the surface, and be sure to put down mats or paper to protect your floor. If you are unable to match the cabinets, or hesitate to change an antique piece, don't be afraid to be bold! Your island will pop as a unique piece if you choose a completely new color or let a beautiful wood contrast with the painted cabinets.
Add a cooking and prep surface. A kitchen island can be used as an eating space or a place to prepare. If the top of your cabinet is finished wood that you trust for these purposes, you may not have to make any changes. Many people, however, add a hard surface like marble.