paris- There is a nice write up by Ben Hiles on the dual caliper set up in the FAQ, just do a search for it. It has pics and everything. I'm currently working on this mod as well. You will have to obtain a second caliper and also the mounting bracket for the second caliper, along with an additional rotor and mounting hardware. I would suggest new stainless steel brake lines for an improvement, HELUSA will custom make the lines to your desired lenghts. I am going to use a master cylinder from an RC51, some people use master cylinders from late 70's Goldwings as they match the bike better (if you care). I would stick with a Honda MC, as then the banjo bolts are the same regardless of what you use.
I think the only major issues, other than the usual ones with making sure your calipers and master cylinder are working properly and the lines properly bled, seem to be just getting the proper alignment for the second caliper (read the write up).
If you need a replacement caliper or second caliper for the upgrade, I actually have one for an F1 that I don't need. Its in good shape, IM me if you want it.