Correct me if I am wrong, but my current understanding is that DVD players can't handle the filesystem of data DVD:s.
I dont know of any standalone dvd players that play mp3s burned on dvd-r, however you can create something similar by using SonicFoundry DVD Architect (part of vegas+dvd) which will take mp3s as source and trancode them to .ac3 for dvd compatiblity. You can also add menu's, title's, picture's...etc. You can download a demo & manual off their website www.sonicfoundry.com