Mike Hughes, user assistance architect at IBM, has written a column on Instructional Text in the User Interface: Some Counterintuitive Implications of User Behaviors. It wisely promotes the placement of instructional text below or adjacent to form widgets and not, as is common, above them. The reasoning is well laid out but it can be summed up with a simple sentence from Mike’s column:
Given a choice between reading and doing, users prefer to be doing.