Hi Twee,
What OS are you using? If it's XP, use Media Player 11. Nero 9 is really not up to scratch in my opinion and causes more problems than it fixes. Media Player or Itunes or Winamp etc etc are all fully capable of converting at the same quality.
Out of interest, why are you converting to 64kbps? If it's for your music player, i wouldn't bother, MP3s at that rate sound terrible, you should be converting them to 320kbps.