Right I'll try and explain this as best I can. Now Polys and SubD can actually be part of the same model. You can basically generate a SubD surface from a Poly mesh (preferably Lo res to begin with) when converting to SubD you can have a choice of two options, you can disply the proxy object (lo res poly object) or you can leave it as it is and use the right mouse button over the Sub D to dispaly your lo object cage over the top. And also display vertices and faces and edges too.

Sub Ds are absolutley ideal for organic shapes, but if doing characters with rigging can be very heavy to animate unless you have a lo res proxy figure displying too. You can turn off the diplay for the SD while animating the Lo Res poly version. All this aside you can choose to convert your SD to a much higher res poly mesh once you have finished your model, you have a great deal of control. The only thing I would suggest is not to texture your object while it is an SD surface but change it back to your poly proxy or base mesh as it is also known and do it on that then convert back and so on. I would recommend looking it up on your maya help menu to get an insight there and get your hands dirty too. There is loads of stuff available on the web too. Check out Bay Raitts Subdivision surface techniques. Hope this helps you a little.

Jango