Yes you can blow your engine using nitrous....but there are many myths behind it and most people don't know much about it.
Nitrous, turbos, and superchargers (SC) can be safe, reliable, and produce substantial hp gains if tuned properly. The myth most people buy into is that it will wreck your engine. Some joker back in the day put way too much nitrous on his car with not enough fuel, which caused detonation.
Detonation is when something beside the spark plug ignites the air/fuel mixture before the spark plug ignites it on the upward stroke of the piston cycle.
Most ECU's can accomodate the air/fuel mixture when using a smaller shot of nitrous. At maximum, you are never to add more than 25 hp per cylinder without upgrading the bottom end and fuel delivery system.
Nitrous is a good bang for the buck. If you are looking to add some decent hp and don't have the cash for a turbo, all-motor, or SC, look into nitrous as an alternative. Look at the NOS (Holley), ZEX, and Nitrous Express websites, they have a great deal of information and an informative FAQ section.