The way I do it is to remove the door and set it down horizontal on 3 or 4 chairs.
I measure the same distance down from the TOP of the door (cuz the bottom of the door may have been cut before) to ensure I get the bottom cut straight.
I put down two 2" wide strips of painter's masking tape along the door to prevent the circular saw shoe from scratching the door veneer, and clamp a straight edge on the door.
Then, I set up my circular saw to cut a 1/8 inch kerf depth just to remove the veneer on the top of the door without chipping it up. (the most chipping occurs when the teeth of the blade are travelling perpendicular to the work. So, by setting up the kerf depth so that the blade teeth are travelling almost horizontally when they enter and exit the work, the less chipping you'll have)
Then I apply 2 or 3 pieces of masking tape to the straight edge and set up my circular saw to cut a 1 3/8 inch deep kerf to just cut through the veneer on the other side of the door without chipping it up. The masking tape holds the saw, and hence the blade, away from the previously cut veneer to prevent chipping it.
Then I sand the cut edges of the door to remove the sharp edge so it doesn't chip.
PS#1: You're not likely to cut into the hollow core of the door, but if you do, you can take the door down to some lumber yards and ask to have it "re-styled". What the guy will do is cut a piece of fir lumber to fit in the hollow bottom of the door, and glue it in place so you can cut another 2 or 3 inches off the bottom should you ever want to.
PS#2: If you have trouble getting the hinge pins out (especially the top pin cuz it'll be rusted from the humidity), just grab onto the top of the hinge pin with a pair of locking pliers and TWIST back and forth while pulling upward. That will cause the rust on the pin and the rust inside the hinge knuckle to wear against each other and smooth each other out, thereby allowing the removal of the pin. And, some penetrating oil will also help, too.
Last edited by Nestor_Kelebay; 09-06-2009 at 07:42 PM.