If you don't know where to start, then the best investment is on books.
Corky Bell's "Supercharged" OR "Maximum Boost" is a must read. I said "OR" because a lot of contents in the two books overlap but "Supercharged" has information specifically written for supercharger users. "Maximum Boost" was written for turbo users. Adding boost means upgraded fuel delivery(injectors, pump, pressure regulator), and computer control (modified fuel map and boost retard), ignition quality(coil, plugs, wires), and some other minor considerations like fuel choice and intercooler piping. It's difinitely more expensive and complicated than just adding a supercharger:)