No MPEG-4 and AAC are not the same.
See the following links ::
[for mp4]*en.wikipedia.org/wiki/MP4
[for AAC]*en.wikipedia.org/wiki/Advanced_Audio_Coding
For your second query,
the best mp3 to mp4 converter is the dbpowerAMP, download it from ::
*www.dbpoweramp.com/dmc.htm
Regards,
Shovik.