FLAC / OGG converting to MP3

[R.L. Reingard]

hello audio geeks
can anyone tell me how to convert filetypes, like

FLAC to MP3
OGG to MP3

soundjuicer helps me to get OGG or FLAC. i can listen them on the computer  
right away. thats fine.
if i want to listen some of them in a portable way, i do need MP3 file  
type.

i did google, but only got to see a lot of stuff that only runs if you  
install other packages (what i do not like to do in the first run,  
especially if they are not even included in universe and multiverse), or  
they run under KDE.

thank you for answering.

René