Do you just tap into your existing fuel line and run it to the plate or what?
Yup, from the schrader valve (test port)
I wan to run the nos at about 125HP would this be OK for a stock fuel system and is nitrous works any good and also is installing a Nitrous kit easy or a pain.
It is always advised that a higher capacity fuel pump be used as an added precaution.
I have never heard anything bad about the nitrous works kits.
Installation isn't hard as long as you have access to tools and some patience. It does take a while to put it in BUT you want to take your time and do everything right, a mistake could be very costly.
A good site for info is
http://www.nitrousinfo.com/