The Warhol Effect:

 
This is a very nice tutorial to achieve the Warhol effect by using Photoshop.
 
http://www.melissaclifton.com/tutorial-warholphoto.html
 
I created this picture using a Marilyn photo, the tutorial and Photoshop 4.0, and I am not a very good Photoshop driver. You may use this photo but don't sell it as your own. I think I'll put it on a T-shirt...
 
My Marilyn using Photoshop
 
Here is the picture after doing the cutout filter but before the other processes. You can use this to make your own Marilyn. You may have to use the Magic selector to eliminate the background (it wouldn't save in this manner for me)
 
Marilyn after background cutout step