Here's a simple trick to create a sketch effect. First, open
the image you want to 'sketch'.
Next duplicate, the original photo layer and hide the original.
Select the copy layer, then go to 'Image/Adjustments/Desaturate'.
This is what your 'Layers Palette' would look like.
Next, duplicate the copy (desaturated) layer. Select that layer,
then go to 'Image/Adjustments/Invert'. Your image will now look
like this. (Don't be nervous, it will look a little odd.)
Now, Select that 'inverted' layer, in the 'Layers Palette', and
from the 'Blending Modes' drop down list, choose 'Color Dodge'.
Below is the 'Color Dodge' image. It should be mostly white. Finally,
have the 'Color Dodge' layer selected and go to 'Filter/Blur/Gaussian
Blur' and toy with the 'Radius' integer. When the photo looks
the way you want it to, click ok. You now have what looks like