Well some of the above is correct. Here is the rest.

A dry kit sprays into the intake system. I do not know where you guys are getting the fuel pressure bump from unless there is some off brand kit that does this. It is usually up to the installer to add on a fuel pressure regulator to raise the pressure. Pressure only needs to be raised a few pounds. A dry kit can be used up to a 100 shot.

A wet kit is usually done via a spray bar that injects extra fuel and NOS at the same time. There is no mixing in adavnce because one is in gas form and the other (fuel) is of course in liquid form. You still have to increase the fuel pressure to offset the added demand from the NOS fuel solenoid unless you run a separate fuel pump for the NOS syatem. The wet kits are also installed around the intake. These kits can have multi-stages and can go up to a 300+ h.p. !

A direct port system is plumbed directly into each intake runner
with a fuel nozzle and NOS nozzle. These kits are the most effecient but expensive. You also need to know what you are doing with these kits because you can melt engine parts down quickly with a direct port system. These kits too can have multi-stages and can go up to 600+ h.p. ! YIKES !

And there you have it your nitorous 101 class is now complete. Hope that helps.