This is what your looking for
http://cgi.ebay.com/ebaymotors/NX-Nitrous-Express-Single-Nozzle-Import-EFI-System_W0QQcmdZViewItemQQcategoryZ33740QQihZ019QQi temZ8074006497QQrdZ1QQsspagenameZWDVW
http://www.nitrousexpress.com/Pages/CustomStage1.htm
You can triger it however you want, typically what your talking about is from hollywood and nobody with nitrous ever uses it that way. It has a microswitch by the throttle body so it knows when your at WOT and will only spray then plus an arming switch so it will only spray when it's armed and at wot. Thats all. You can hand triger it with a button if you want but thats so F&F. Nobody with real nitrous systems acctually do that.
Nitrous is the "Air" you always add fuel.
Dry kits (unlike what I posted) still add nitrous to the intake but double up the fuel pressure at the FPR to add the additional fuel.
Wet kits spray both nitrous and fuel through the nossle which is the best way.
Direct Port kits has one nossle per cylinder and drill into the intake manifold. Unless your spraying big, you don't need it.
The Single nossle wet kit which I have shown is the most reliable best HP producing way to make power. NX guarantees with in 2% of the claimed HP output at the wheels. Meaning if you have a 50hp jet in the system it will make 50hp or damn close within 1 hp at the wheels. It does too, I have dyno tested it on 3 of my cars with nitrous and trust me, the power really is there.. My 100whp shot made 99hp and 144ft/lbs of torque which is huge. Ran it all the time on my GTI.
Here are pics of my Direct Port system. Notice each nossle has two lines for nitrous and fuel. The wet kit is the same but one nossle into the intake pipe not 6.
Yes I made all the lines and did the whole system myself. Thats a 75-150hp setup there. I sprayed everything from 75 to 150 on it too. Not over 100 with pump gas tho, used 117 for 125-150hp shots. There is acctually a carburated regulator before the fuel solenoid there (in red) and I reduced the FI fuel pressure to carburated levels and ran a larger jetting pattern for a wider ranges of hp levels. Kinda hard to explain if you don't know nitrous. People who have lots of nitrous experience really appreciate the system for it's compleity yet being utterly simple.
I'm somewhat of an authority on nitrous if I do say so myself.