Who does one write to at Apple to get the tunes back that you have purchased from Apple after a crash. I know that a lot of people have done this. They have said Apple will do it.

Here's the FAQ for getting your lost downloads back:
http://www.apple.com/support/itunes/store/download/

for uncompleted downloads:
http://docs.info.apple.com/article.html?artnum=93015

if it downloaded but your computer crashed after the download, the music file may be in your library, just not in the index. Look for it in the iTunes library/Music file.

As a happy iTunes customer, I make a very simple backup of my tunes: I burn them to Audio-CD, print a booklet and put the CD on the shelf in my living room.

You can, of course, copy the iTunes library (~/Music/iTunes) to any backup device of your choice. If you change your computer, don't forget to unregister the old one with iTunes before you take it out of service. If, after a crash, that's impossible, you should be able to sort it out with Apple support.

They'll usually only let you do it once so when you get it back, make backups of it.

Get yourself an external (they're cheap right now) and use either Carbon Copy Cloner (http://www.bombich.com/software/ccc.html) or Super Duper (http://www.shirt-pocket.com/SuperDuper/SuperDuperDescription.html) and make boot able backups of you system that included all of your data. It's foolish not to have a backup plan today with the vast stores of data we all now keep.

My iTunes library is on an external HD. iTunes only works when its plugged in but I can live with that.