Gears give you car a mechanical advantage.
It requires less effort to move the vechicle, at the expense of higher engine RPM at a given speed.
I don't know what kind of car you have, but if its a V8 car, its more than likely a 8" rear end. Gear sets usually run around $150-200 a set. Its recommend you have a professional install them for you as you don't appear to have any experience installing them. Total cost should be around $400 depending on the shop.
You will still have a 3 speed tranny. You will notice higher rpms at freeway speed and typically a drop in fuel milage as well. Accleration will improve greatly however
[color:red]1966</font color=red> [color:blue]V8</font color=blue> [color:red]Coupe</font color=red>
5 speed, 4.11s, 10.13 in the quarter mile.
Oh wait, that was a Sammy Haggar song...