Its simpler than it looks. There are various vfaqs for different model DSMs, but read them all since some are better at explaining certain aspects of the job IIRC.
This is basically what it is. The stock wire is too small. You run a larger wire from the battery, and control it with a relay. The trigger for the relay is the stock wire, that way it comes on whenever the ECU tells it to, just like stock. So on the power terminals (normally open) you have the large wire from the battery, and the large wire to the pump. On the coil terminals you have the stock wire on one, and a ground on the other. You should also rewire the pumps ground wire, I tied mine to a rear seat bolt with a ring terminal. Thats all there is to it. The hard part is getting all the wire colors in the stock harness back there so you know what wires to use, and gathering all the little terminals and things you need. Anything larger than the stock 18 guage crap will do, but most people do 10 or 12 guage because its plenty large and easy to find. Some poeple even buy a 15 dollar amp install kit at walmart, since it comes with the 20 feet of 10 or 12 guage wire, and some crimp on terminals. The relay is about 5 bucks, just a standard bosch automotive relay, like one you'll find in the fog light section at an autoparts store. The vfaq should have a few pics of it, maybe a part number.
HAve fun.
Its a pretty easy job, just take your time and do it right. Crimp everything tight, and tape things up well, etc.