Step One: If it's an old car, check all rubber on the cooling system. That is the hose coming out of the top of the radiator, out of the bottom, and into and out of the engine. A pretty safe bet is if one is bad, they all are. Normally if one is cut, you just fix it, but if they are all rotten replace all rubber.
Step Two: Start stripping! Take all of the interior carpet and seats out, but leave the brackets for the seats in, take out the back seat, but save it all. Take the door panels off, and take out all bolts, this should make the windows able to come out. If you break them, you just have a mess, so dont do it! Windshield and panel windows not in the door are tougher. Cut all the weather stripping back with a knife. They make special ones for it, but a utility knife will do. Once you have the rubber weather stripping off on the outside and inside, get in the car and push gently on both edges of the windshield with your feet. Hopefully it'll pop out for you. I have helped prep two cars and its worked for me just fine.
Step Three: Switches. You wouldnt believe how much wire is in a car that you dont need. You just have to find the two wires that go to the starter, and the one that has to touch the battery. I bought a metal toggle switch, and a pushbutton starter switch for about $5 at the auto parts store, and had them wired with spare wire in about 20 minutes. I ran the switches right next to me, and put them on the passenger seat rail, which has no seat on it (since you removed it!) so you can have access to start your car when strapped in.
Step Four: Battery. Build a box made of wood for your battery and bolt it to the floorboard of the passenger seat. Make the box big enough for the largest battery you have, so you wont have my problem and try to put to big of a battery in a box. Stick the terminals all the way through the firewall in any hole that they will fit through and stick them on the battery. If they are too short, get new cables and put them on.
Step five: Gas Tank. Unbolt your original gas tank, you cant use it. Get ahold of a metal boat tank, and take the back seatbelts, or the seatbelts from another car and bolt them right behind your driver seat. Put a piece of foam down on the floor, then the tank, then a piece of carpet over top, which strangely enough works for a firewall at my derby, then use the seatbelts to secure the tank to the floor.
Step six: Welding. You need to weld doors shut. My derby wants cars to be as stock as possible, so you cant strengten anything. You can put a pipe where the dash would be, under the windsield, and another behind the drivers seat going post to post, to keep the car from crunching in. Get someone with a welder to do it for you, or learn how... its not too hard, and it all depends on your local rules how you should do it.
Thats about it... anything you want to ask, email zjm1000@hotmail.com and put derby as the subject so i know to read it. ill try to help the best i can.