The main things you'll need are a 6" piece of THICK PVC pipe, a 15-25 watt bulb (you can go as high as 40, but the base can get pretty hot at 40), and "pearlized" liquid handsoap that contains glycol stearate or glycol distearate (should be listed on the ingredients of the bottle). Avoid anything that has moisturizers or additives like aloe, etc. Click on the pictures for a full list of the supplies I used.
Step 2: Build the Base
Sand off and trim any plastic leavings on the top and bottom of the PVC pipe. Notch the bottom of the pipe for the cord. You can glue the bottle to the base, but I recommend using an old mouse pad and fashioning a rubber seat you can place the bottle on and glue the ring to the top of the PVC pipe. See pics for illustration.
Step 3: Prepping the Bottle
Soak off any labels in soapy water and rinse thoroughly. Fill the bottle about 3/4 full with warm water. Add 7-10 squirts of the handsoap, screw on the lid and shake well until the soap is mixed. Then "top off" the bottle by adding water to about 1" from the top. (This allows for air expansion as the bottle heats up). I recommend creating a rubber seal for the lid by cutting another piece of the mousepad you used for the base. Cut to fit inside the lid. This helps insure that no water leaks out of the top.