Can anyone tell me what the difference between a MP3 and a MP4 is? Basic answers only please!

I have an iPod video that cost $220 with my own money. I am so worried that Im going to lose that and that will be a waste of $220. I need an MP3/MP4 so I can carry it around at school and so if I lose it, its easy to get another one cheap!
I want/need a MP3/MP4 that:
* holds at LEAST 250 songs (around 350 maybe)
* that has a strong recorder (optional)
* FM radio (optional), record FM stations (optional)
* it needs to be small (smaller then iPod video!) and lightweight
* needs to have an organized screen (should have someway of getting to a song without going through every song).
P.S. The “optional”s I have never had on an MP3/MP4. The system doesn’t HAVE to have it, it would just kinda be cool!
Thats really all! Oh yeah, the computer that I have is a MAC, I have a windows downstairs, but I use the MAC more often. Please think of a reasonable price to match paragraph 1.
Thanks
2) I have one more Q, what’s the difference between an MP3 and an MP4?

whats the difference between mp4 and mp3? And is there such thing as a mp4 Ipod, if so, how much does it cost?

I bought a MP – F988, a MP4 player according to the salesperson 8 months ago. Happen to see it on internet but it is classified as MP3 player!
The one I bought support motion pictures( like .avi format), recording and other functions which normally see in a mp4 player. I guess that’s why it is called mp4 mp3 player .
But anybody know what’s the major difference between a MP4 Player and a mp4 MP3 player?

MP3 is an audio format only, and the name “MP3″ has incorrectly come to mean a digital music player. It was invented in late 1980s. MP4 is a “container” which means it can be a video file, or an audio file. The songs sold on Apple’s iTunes Music Store are in AAC format.

I found this website below that has really low prices for MP3 and MP4 made to look like IPODS and are really cheap. What do you think, too good to be true or will it work fine? Also I’m not sure what the difference is between mp3/mp4. http://www.davismicro.com/

An MP3 okayer is more geared towards MP3′s whilst an MP4 player can play, surprise, surprise, MP4′s which are video audio files, well compressed.

BOTH ARE SONG FILES ONLY MP3 IS QUITE FAMOUS AS U KNOW
MOST DATAS ARE IN MP3 FORMAT ONLY
MP4 IS NOT A GREAT HIT
IT IS ACTUALLY MORECOMPRESSIBLE IN MP4 THE SAME SONG IN MP3 WOULD BE SLIGHTLY BIGGER
BUT MP4 IS NOT A GREAT HIT COZ ALREADY MOST DATAS ON WEB AND CD’S HAVE ESATBLISHED THEMSELVES IN MP3
IF U R PLANNING TO BUY A MP4 PLAYER I REQUEST YOU NOT TO BUY NOW.
THANKS
UR FRIEND

mp3 player-plays music
mp4 player-plays video (along with music)

Can they play the same music?