Hey Stu,
Your work is amazing by the way. I think my jaw drops everytime I see it. Basically I start off with a low poly model of about 7,000 polys that I made in XSI. I made it in XSI because I can do it faster in that package and XSI handles polys by being very light and fast. I also own a commerical copy of XSI too so that is a part of the reason too. I make an organized mesh in XSI because although ZSpheres are cool they do not give you an organized mesh. I have also learned the hard way not to do detailed organised meshes because then you lose flexibility which is reall important in modeling and I also can't reuse the model as much or as easily. Then I export it to ZBrush and double my ZBrush Document size and then AAHalf it then zoom it. I load the character tool and go into the edit mode and just start dividing the model up to about 5 or 6 times. I tend to use the standard and smooth brushes the most, then the inflate and pinch brushes next.
For more of the art side I have been studying Anatomy for the last 3 months like crazy. I am drooling over this particular model and I plan to get one in the near future.
Muscle Bone Model
Also I bought 16 figure drawing books for reference plus I already had the Primal Pictures CD set which is excellent and I use it on a regular basis, and I highly recommend it. These prices are based on Amazon.
1 An Atlas of Anatomy for Artis $10.36 1
1 Drawing the Human Head $13.57 1
1 Dynamic Anatomy $15.72 1
1 Dynamic Figure Drawing $13.57 1
1 Dynamic Wrinkles and Drapery $15.30 1
1 The Figure in Motion $13.57 1
1 Artistic Anatomy $15.72 1
1 Drawing Dynamic Hands $13.57 1
1 The Artist's Complete Guide t $22.05 1
Also Some Good Links with This Regard:
http://www.artnatomi...t/uk/index.html
http://www.reybustos.com/04er/er.html
http://www.reybustos.com/03ra/ra.htm
Basically I work on the Torso first particularly the back and then the Chest. I think I start of the back first because it always gives me more trouble than the chest and stomach. Well everything branches off of the chest and the back so I just kind of bounce around between the legs, arms, and the neck shoulders and head. I do the hands and feet last because they have the least overall impact on the model as a whole but make a big difference with the arms and legs for everything being layed out right and weighted properly.
Then once I have all of the forms layed out I do fine etchings with a very small brush and set the strength of the brush pretty low. I go back along the edges between the masses and cut in lines along the form and then go back and smooth over them. This allows me to basically highlight these forms in the modeling process long before I ever get to the actual shading. After I get all of these masses properly layed out then I go back and detail. I make the model then not quite symmetrical and I add veins and skin pores and such things like that. I don't use projection master for this detailing stage. I like having that fine control right in my hands to define exactly what I want it to look like.
I do skin pores by changing the edit curve so that it has noise in my brush and I set this value fairly low. I change this value based on where the skin pores lie because skin pores vary based on the various areas of the body.
To be honest I will probably ditch XSI for most of my modeling when ZBrush 2.5 comes out because I can then make organized meshes very quickly that I can then load into Houdini. Where I use Houdini for modeling will be for the procedural aspect of modeling so that I can quickly alter forms and rig and animated based on presetup digital assets so that I can get a fast turn around. Basically the XSI and ZBrush are just building Blocks for Houdini.

I can gernerally create the forms faster in other packages but once I have these basic forms I can manipulate them far better and faster in Houdini so that is my preference.
I will still keep XSI around when ZBrush 2.5 comes out for Mental Ray, Game Real Time Shaders and some other aspects.

More and more of my pipeline however in the near future will be ZBrush and Houdini.
In a couple of months I am going to post a Zscript that will show my modeling process because several people have asked for it on the ZBrush Forums. I am just going to model the patella which is a small bone but it will show my workflow which will probably be useful to some people. So if people want I will post it here also.
I hope I answered your question if not feel free to ask away if I glossed over anything. Again I love your work man.
Cheers,
Nate Nesler