how to select part of old mp3 and create new one

[Long Wind <longwind2@yahoo.com>]

i want to copy part of old mp3 file and create a new one

at first, i install lame, but it doesn't seem to have such ability

i try mencoder, it doesn't either

then i try qmp3cut, it says "no valid header found"

though i can play the mp3 file and it's OK

what should i do next? Thanks!