Along with the requirements definition phase (See my post of July 15, 2006.), the traditional next step of IT staff and consultants when they choose software is to extrude a request for proposal. The RFP outlines the presumed requirements of the department for the software. It is more detailed than a request for information (RFI).
Unorthodox I may be, but my view is that RFPs consume far more time and cost and effort than they return in insights. Their pages of questions put vendors through agonies and then spill out in an enormous matrix that makes it difficult to narrow down the list of candidates.
A better procedure is to pick a handful of crucial aspects of the system and, after having seen initial demos, ask the vendors to respond in just those few areas and with thoughtful, complete responses. You can do this process two or three times as you narrow down what is important, set priorities and scale those attributes, and come to realize what few important factors differentiate the contenders.