Ok, I've looked this over and unless I've missed the boat (entirely possible!) I don't think this is what I was after.
Looks like this creates in the root project directory and places the drawings in the subsets in them just like vanilla Acad.
You appear to have ADT/MEP, so let me try to explain better.
I'm using the Project Navigator and my project path is O:\Comm_Custom\enu\test proj folder\9A677-A. By default the PN places sub-directories in this project folder, one of those being Sheets for storing... well.. Sheets.
When you create a subset by right clicking on the root sheetset and select new and get to the subset properties dialog one one of the options is a check box to "Create folders relative to parent subset storage location", if you select this check box the new subset will be created, and a new directory gets created under "Sheets" that any new sheet drawings in that subset will be stored in. So if were to manually create a new subset called "Submittal 8.5x11" with the "Create folders relative to parent subset storage location" selected I would end up with a new folder O:\Comm_Custom\enu\test proj folder\9A677-A\Sheets\Submittal 8.5x11 that any sheets added to that subset will now be stored in.
I cant figure out how to get this done with VB, get the folder (subset) created and have the PN recognize it to dump sheet drawing into.