how do i get a regular mp3 player (not ipod) to play through the front aux?

Go to Radio Shack and buy a 3.5mm (headphone type) audio cable with male connectors on both ends.

http://www.radioshack.com/product/index.jsp?productId=2944877&cp=2032054.2222882.2224127&allCount=109&fbn=Type%2FDocks+%26%23038%3B+cables&f=PAD%2FProduct+Type%2FDocks+%26%23038%3B+cables&fbc=1&parentPage=family