Get a product called "Goof Off" from the hardware or paint store. Make sure you get the kind for latex paint. Test a small area to be sure it doesn't cause a problem with your wood as it is impossible to tell what kind of finish it has. I have had good luck with this. If the paint is really stubborn, you may have to use a nonabrasive pad such as a Scothcbright pad.
Here is a link to the product page: