SubDStroke provides an easy way to partially subdivide a model.
Partial subdivision can be useful if you want to add detail to some parts of your model while keeping the overall poly count low.
Press the button immediately after drawing a stroke on a polymesh in Edit mode and the stroke will be subdivided. Pressing the button again will further subdivide the stroke.
If Ctrl+drag was used to paint a masking stroke then the whole masked area (including any previous masking strokes) will be subdivided. Only one level of subdivision is possible with this method.
Note: the SubDStroke button must be pressed IMMEDIATELY after making a stroke. If the model has been rotated, scaled or moved the subdivision will not work. (This is because ZBrush regards any mouse movement on the canvas as a stroke.)
SHIFT-click the SubDStroke button to UNDO the partial subdivision. This must be done before the model has been modified further.
Unzip the zip file to your ZStartup\ZPlugs folder ..\ZBrush2\ZStartUp\ZPlugs). The plugin file SubDStroke.zsc and the folder SubD_data should both be in the main ZPlugs folder. You may need to create the ZPlugs folder if you have a new installation of ZBrush.
Restart ZBrush. You should now have a SubDStroke button in the MarcusTools subpalette of the ZPlugin palette. You may Ctrl+drag the button to a suitable place on your interface and save the position by storing the UI configuration (Ctrl+Shift+I).
Updated August 18 2005
Again ... I hope I have now fixed the feature whereby some strokes were not being subdivided. You should be able to use any sort of stroke, including ones modified by Ctrl, Shift or Alt.
Mask2Group plugin added
Lemonnado suggested that a button to make a polygroup of a masked area would be useful, so I have added a plugin for that too. Just unzip to your ZPlugs folder as above. Press the button after masking part of a polymesh and the masked area will be made into a group.
I hope you find SubDStroke & Mask2Group useful.