My old mp3 player does not support ogg format.

Install gstreamer0.10-plugins-ugly-multiverse with apt-get, which contains the lame plugin for gstreamer.

Then follow the instructions at http://www.emcken.dk/weblog/archives/99-MP3-encoding-with-Sound-Juicer.html, you could create a new profile rather than change the existing "CD Quality, Lossy" profile. Or you could follow the online-help of sound-juicer in "Preferences" section.