Distributions of regular branched surface coverings

In a study of surface branched coverings, one can ask naturally: In how many different ways can a given surface be a branched covering of another given surface? This problem was studied by many authors in Quart. J. Math. Oxford Ser. 2 46 (1995) 485, Math. Scand. 84 (1999) 23, Discrete Math. 156 (1996) 141, Discrete Math. 183 (1998) 193, Discrete Math. (in press), European J. Combin. 22 (2001) 1125, Sibirsk. Mat. Zh. 25 (1984) 606 etc. In this paper, as a complete answer to the question for regular coverings, we determine the distribution of the regular branched coverings of any nonorientable surface S when the covering transformation group and a set of branch points are freely assigned.