Select
all verticles, duplicate them, symetrize
by "Global X", join the two
halves (you can also use Mirror Modifier
in modifiers stack).
When
the main model is ready, you should do UV
Mapping. In Blender it can be done very
simply and fast. Just mark thee seams like
shown below, go to UV Face Select mode,
press [U] in 3D View and choose "Unwrap".
Export
the model to (Wavefront-) OBJ file (if
you have the Linux version, download
the script from Blender.org -> Python
Scripts). Import it to ZBrush, check
the mapping ("Uv Check",
then "Fix Seams").
Now
it's time to give the head its basic
shape. Multiply the polygon amount by
pressing "Tool -> Geometry
-> Divide" and use the "Inflat"
tool ("Transform -> Inflat";
in "Edit" mode).
