I would say more difficult than you realize if you want to do it correctly. Like any forced induction system, it is highly recommended that you drop compression on your car (and make sure that you have forged pistons), and go with a milder cam (than you would with a normally aspirated engine). Turbocharging is very hard on pistons (especially if you plan on adding NOS to this mix).
Another thing that you need to consider is where the turnochargers will be positioned underneath the car. If it is too close to the floorpan, you will run into some serious issues... like setting fire to your car.
You also want to invest on high quality waste gates, and pop-off valves. Don't scrimp on these components.
You should also research the types of turbochargers that would work best for your application(s). For road racing, you wuld probably go for a smaller unit with big intercooling. For drag racing you might go with a bigger turbocharger (like a pair of Garrett T-66 or T-88). They tend to have less turbo lag in comparison to the smaller units. The larger ones will not hold up as well in a road racing situationn at high prolonged rpm's.
The other issue is intercooling. If you choose not to intercool your turbocharged system, you will essentially lose half of your power increase when the car warms to running temperature (the same goes with non-intercooled supercharger systems). For big applications like V-8, it ii usually recommended that you use a air to water intercooler. This is where the costs go up on a system, and is a pretty critical component. You want to invest in the most robust intercooler that you can find.
Finally, I would highly recommend that you start this project with a fresh engine. Turbocharging will stress an engine quite a bit and many things that are worn can let go with the added stress.
The turbocharger experts can go on for hours on this subject alone. I personally am not a big fan of forced induction because of the durability issues that arise with them (versus normally aspirated engines). I hope that this helps. Good luck in your search.
Brad