Cranker-
I have a older Dodge with the Cummins and I looked into the propane injection as a way to wake it up. After I looked around and called a few of the manufactures I got some what of a basic understanding of them.
Most of them are pretty simply and are operated off of the boost you turbo puts out. I bieileve they have a line running from the intake (boost side) to a regulator that is proportioned to your boost. Some are not though and once you hit the switch you get a preset amount of propane. I heard these are hard on drivtrains though.
It does supposedly increase your range of mileage, pending on how much you use, but some people on a Cummins forum claim up to 5 miles per gallon if they use about 20 gallons of propane per tank of diesel. It does give you power of course, quite a bit, and the kit is pretty simple, a regulator, hose and some electronics to activate the bootle on and off with the keyed switch. The known drawbacks are, higher EGTs, and of course having to locate a spot for a tank, filling it, and hoping you never get hit in that spot in a accident.
If you really want to know alot about it, search for any popular diesel forums such as Powerstroke or Cummins, and there is thousands of people who have information. Bulldog, a manufacture of one of the types out there was at one of these forums, and sent me information about it. Hope this helps.