Regarding procedures -
If you register for cs executive before 28 feb you can appear for both goups in december 2010 whereas if you register after feb but till may 31 you can give one group in dec 10
For ICWA i dont know details but i think you have to apply till june end for dec exam. dont know whether for one group or both. Refer website for details.
Regarding choice, you can go for m.com + one from cs/cwa.
From time point of view cs can be completed early as it has 15 months training compared to 3 yrs. of icwa. Instead of scope, you should choose as per your interest. CS will have more focus on legal subjects whereas CWA will focus on costing field. Study the syllabus of both courses and then decide. If you dont have keen interest in m.com you can drop it from your list and can go for both cs/cwa.
www.icsi.edu
www.icwai.org