PART I

First you have to draw a profile of the head you want to model. I usually choose one form a picture and rotoscope it in Softimage.

Draw the top part of the head profile from the inside of the mouth to the back of the head, b-spline.
Duplicate that profile and move those points to draw the other side of the profile, as seen on this following image.
Each of the two splines of the profile should have the same number of points, between 20 to 25 per spline.
Also the steps should be 3. "Info Selection Steps 3"
Next, get a B-spline circle with 15 points and also 3 steps. The steps help keep the geometry down.
Until now everything should look like image 1.

Next you have to Guided Extrude these three splines.
"Select Surface-- Guided Extrude ЕЕЕ select Scale Width and Height"
When prompted, select first the circle then the top spline and finally the bottom spline. The result should be something like Image 2.

Turn "Preferences--Create Modleing Realations" on. Extract the splines of only one side of the head. Select Draw-- Extract and select the object; press on the top-center spline of the object to extract it. Select the object again to extract the sencond spline next to the first one.
Do the same until you have extracted all the splines from one side of the head. Then you have to delete the original object and skin "Surface-- Skin" the splines.
Surface--Skin Select the splines from top to bottom one after the other until they are all slected, then press the right mouse button and choose b-spline and 3 steps when prompted.
The result should look like image 3.

If you look at the top view, you will see some points crossing over the z-axis, those points need to be brought back to the positive side of the z-axis.
Select the original splines of the half head, tag those points crossing over, and move them to the so it looks like image 4.

Just by tagging those points the first result is something like the next image. Which is beginning to look like a real head.