Grim,
Prowls are in several formations, like 1-5-5, Dime: Normal, and Nickel: Normal. All the "prowl" means is that the players are in 2-point stances; almost like they are hovering. They move/float around pre-snap to confuse the OL.
The 1-5-5 prowl is much the same way, in which the DT is in a 2-point stance and floats around; as do the linebackers.
The Green Bay "Psycho" formation is your typical 1-5-5 in which your nosetackle lines up in a 0-tech (heads up with the center) in a 3-point stance. This allow you to EASILY dictate which side you can adminster the pressure from, as you know that the center cant afford to slide protect without giving the NT a free run (or a 90% free run with a light nudge from a OG who can barely reach him) at the QB.
Prowl formations are a little less predictable as to where your pressure might come from. A number of factors affect it, and whether or not it works. Snap timing by your opponent is a key factor. One play he may snap it with the DT floating in a 1 technique, the next, he may be 2i...where your floating DT is affects how the OL can pick up a specific play.
Portal 
