Okay step 1. Make a new file in photoshop with the above settings, 640x480px, 72 dpi
step 2. Draw some random blobs in the file with a standard black, round brush. Just like the picture.
step 3. Go to Edit>Define Brush Preset. Click okay
step 4. Open your brush settings (Window>Brush) and input the following settings. Spacing: 1%; check the 'shape dynamics' box and check the 'other dynamics' box. Click on the little square in the bottom right to create new brush.
Then draw with it You'll find it makes sorta half decent hair. Change the brush size for different size strands, go from darker to lighter colours and when you're happy then use a 3px standard round brush to add some dark and light details.