i did on your previous post.
try k3b or eroaster. if you don't wanna do that, gnome toaster may require you to manually decode the mp3 to wav. x-cdroast requires this, but i don't use gnome-toaster so i don't know if it really is this way too. if you have to manually decode mp3 files, you can use lame from the command line. or you can add "lame --decode" command to the mp3 filetype association and select mp3 files and right click on your selections and do an Open with, or you can run an mp3-wav converter (lame wrapper) that i wrote.