Actually Nitrous isn't flammable. Would even blow with a spark. Nitrous is an oxidizer. The oxygen density in a molecule of N2O is higher then in air compressd by a strong blower. Throw in enough fuel to be stoic and you have a much bigger bang.

This issue with nitrous is you introduce a piss-ton of power. Nitrous is a torque builder. Regardless where you are in the power band, you can add a ton of torque with a nitrous shot. If you're too low and the engine isn't free to rev, you can apply enough power to the piston that things start to break. However, this does not mean you can't boost at low rpm. I have seen several systems that are progressive nitrous. Most are direct port and use auxillary injectors to basicly run the nitrous in tandem to the MPI fueling. The amount of nitrous is controlled by a computer reading the same sensors that are determining fuel injector pulse width. So at low rpms, a small amount of nitrous is being injected. Enough to boost the torqe and supply a good power increase, but not enough to break something. As rpm increases, the amount of nitrous increases.

These systems are costly and very advanced. They also require a large tank as they are not small single shots used a a/4 mile at a time. So in short you can build a nitrous system to do what you want it to do. You just have to know what you're doing or find someone that does.

The only bad thing I do see about the X when it comes to nitrous, which will be a MAJOR problem, is that it's DIS. Since it uses a coilpacks controlled by the ECU, you can't install an aftermarket ignition controll or even higher output coil. To safely run nitrous you really need a stronger spark controlled by an ignition that you can manually, on the fly, retard the spark timing. Running too advanced spark timing while spraying can lead to detonation which is very very bad. You also lack a way of bypassing the stock rev limiter. The stock limiter works by cutting fuel to random cylindars. A digital ignition will just cut spark. Hitting the limiter and cutting fuel while spraying will in effect cause the worst possible lean case you can imagine. This equates to holes burned in cylindars.

So nitrous in an X-terra could be done. It could be done to assist in even rock crawling and boosting low end torque. However you won't be able to just throw on a dry kit with a WOT or "go" switch and call it a day. It will take planning and money, but if done right will leave you very happy.