check if it's getting gas by pulling the hose off the fuel filter (a cylindrical piece near the fire wall with hoses coming out each end) and that it's getting a spark. to check for a spark, i usually will remove a spark plug wire and insert a long screw driver in the wire, and rest it on the valve cover, or just a very small distance above it. then, have someone crank the motor, and you should see a spark jump. if either of these aren't working, that's why the car won't start. otherwise, i doubt it's even turning over at all. maybe you think it is, but that metallic knocking is actually the engine getting stuck somewhere, and though it may sound like it's turning over, it actually keeps getting knocked back.
swapping an engine depends on how your mechanical ability and tools are. you'll need an engine hoist. you'll need to raise the engine and transmission, remove them from the car, d/c the tranny, and connect your new engine, then return to car. if you check out the autozone online guide, you can get a good idea of what it takes. if you don't have a lot of experience working on cars, i definitely wouldn't recommend it. there are just way too many things to screw up and too many places to get stuck.
