what version of itunes and with what OS?
I had that problem on my ipod and I repaired the database using iPodRip. Also somethings that cause it on an iPod are low battery life and bad sectors on the hard drive.
As far as iTunes upgrade to 4.6, run diskwarrior, drive10 or techtools if you have it. Do check the start and stop times of the songs. if it's more complex then that, Backup your iTunes library file it should be about 6 to 9MB and then reimport all your music by adding your iTunes Music folder to iTunes again so it remakes the library file and processes the songs again. if you are concerned with playcounts and ratings, use iPodRip to get your songs back in iTunes for it copies not just the song but the library file info too.
Instead of sending someone else an mp3, the start and stop time is in the iTunes library file. download
another player and try that file with it if it still stops try copying the file somewhere else like to your desktop then try it. Just use itunes until you notice a song stop then mark it in comments. and make a smart playlist to find all the songs with that comment.
That is if you use a mac. if you use windows try as suggested
MP3Utility. this is what my friend uses but I am not sure if it's the same as suggested.