shrinking the file size of an MP3 involves 3 things:
1) cutting the mp3 into portions-ergo getting only specific portions of the song
2) decreasing the bitrate or audio quality-example a 5mb song at 320kbps may only be 2.5mb when compressing it to 128kbps, further size compression means lower quality(worse sounding mp3s)
3) converting it into a different format-WMAs are half the size of MP3s meaning a 5mb 128kbps mp3 is 2.5mb-3mb if compressed to a 128kbps, you can slo convert mp3 to AAC for ipod play