Awarded September 6 2006
I first enlarged my source photo to 4500 pixels high at 300dpi. and saved it as a jpg. On a new layer I traced the main outlines of the face. On another new layer underneath that I painted the base skin tone and blocked in the basic tones of the eyes and lips with a large hard-edged brush at 100% opacity..Above that layer I made a new layer for the base hair colour and blocked in the darkest hair tone with a hardedged brush at 50% opacity which gave me a variety of tones - use the brush in the direction of the flow of the hair. Saved the image as the first stage.
With the outline layer still switched on as a guide I started to model the skin tones - on a new layer above the skin base layer- with a large soft-edged brush at 29% opacity. In this case I started with the darkest tones - using it so transparently allows you to build up darker and darker tones.

By having the source photo the same size as my painting of it I can use the Window/Arrange/Match zoom and location command in Photoshop to zoom around the image, matching an area of my painting with the corresponding area of the photo.

Here I'm adding some mid tones and highlights on the same "skinpaint" layer sometimes sampling areas from the photo and at other times using colours from the swatches.Still using the 45 pixel airbrush at 29% opacity.

 
Airbrush tool adding more detail, varying the size of the brush - getting smaller to add sharpness and detail
 
I'm afraid I got a bit carried away painting the hair and forgot to save it's various stages! But I had too much fun painting it! It is painted on a new layer above the hair base layer. I began with a large airbrush at low opacity using a mid grey working up to smaller and smaller brush while increasing the opacity. Lots of blurring and using the dodge/burn tool. Using the dodge tool set to highlights on a strand of mid grey hair brings out spots of highlight. I'm afraid I worked completely intuitively on this, always referring backwards and forwards to the source photo.
A happy accident playing around with the flow jitter in the brush dialogue! I found turning the flow jitter right up produced these alternating highlights in the brush line.
Starting to add detail and texture to the skin using a very small soft-edged brush at low opacity. It was about here that I started to also use a small hard- edged brush, again at very low 16-20% opacity, and using the alt key to sample midtones
 

Eyebrows and eyelashes on a seperate layer using a tiny brush at 60% opacity.

Standing back to check the tonal values still somew work to do on the right cheek and forehead.

 
Eyebrows blurred a little - with the blur tool
Starting to soften the shadows using a hard-edged brush - very loosely scribbled - at low opacity with the alt key sampling for mid tones
Added a light blue over the existing skin tones on the cheek with a small hard-edged brush at very very low -6% - opacity