As Tony mentioned you can transcode with Lame. Here's the batch file that I use when I want to add songs to my flash player. Change the paths accordingly. You can adjust the parameters to dial in size vs quality. Google for the correct syntax.

for %%f in (*.mp3) do lame.exe -h -V7 --vbr-new -q0 --lowpass 17.5 --athaa-sensitivity 1 --mp3input "N:\Various Artists\Mo Music\X\%%f" "N:\Various Artists\Rio\%%f"