I've got about 40GB of music which I converted over time at WMA @128kb. In order to make more room I want to reencode them at 96kb, preferably without going back and re-ripping from CD's. A few questions:

1) Am I better off staying with WMA or should I go OggVorbis or whatever?

2) The reason for this thread, most of the programs that I have will only reencode 1 track or file at a time, this is hellish. Does anyone know of a programme (preferably freeware) that will batch encode everything? The idea of just clicking once and then going away for a day or so is attractive to me.