i havent used mp3 trim myself, but judging from what it does you should be careful as to what files you work with, as i'm sure not all your songs have the beginning silence.
i think there is a winamp plugin in their latest release that ignore silence.
but you're trying to reduce hard drive space right? if it comes down to it, you can edit the mp3s in sonic foundry's acid. it doesnt take long at all since they work with mp3s.