Is there any way to split a optical cord going out of my stereo into my cable box and dvd player. My stereo only has 1 optical output

You don't want a splitter, but rather an optical switch:

http://www.monoprice.com/products/product.asp?c_id=104&cp_id=10423&cs_id=1042302&p_id=2946&seq=1&format=2