Software to loop sections of MP3's ?

Maybe this stuff is out there everywhere but I can't find it. I am looking for something that can loop any section of an MP3 so I can just play it over and over. Preferably free stuff 8-). What should I get ? Where should I look ? I am new to this board but I was thinking you guys have got to have stuff like that to break out sections of songs to master them. Thanks... awesome site.