People have been asking for a tutorial on this, so here we go. I'm pretty sure that this isn't the way you're supposed to vector, but this is how I do it. It's very simple, but it might be easier if you have some basic PSP knowlegde. This is the image that I'm going to be using:

1. Make a new raster layer. You're going to need to make a new layer for every separate part of the vector. I don't want to have to repeat myself every time.

2. Take your freehand selection tool and match your settings to mine:

3. Select around the face then go to Selections >> Modify >> Smooth. Set both to 10 and check the box for Anti-alias and Preserve corners. Click ok.
4. Now take the fill tool and fill your selection with the color of the skin.
5. Do the same thing for the hair. In order to see the picture better, you can set the layer with the face to invisible by clicking the eye next to it on the layers palette.

6. To make the hair more realistic, just select little lines and fill them with a darker or a lighter color.

7. Just repeat those steps for all the different parts of the picture (the arms, the shirt, etc.) To separate the neck from the head, just use a color that is slightly darker than the color used for the face.

8. After you're done with all that, make a new raster layer and drag it right above the base picture. Fill it with a color or a pattern and there you have it! Your very own vector.