Help picking out my car audio system?

[Down With The Clown]

Okay, I get my license in about a month and I have a car. It's a 97' Buick LeSabre and by the time I get my license, I'll have AT LEAST $500 and I was going to put it all towards my car audio and stuff because the stuff in there sucks. I was looking on BestBuy.com and I don't know what to get and what does what; There's the stereo, speakers, amplifiers, and subwoofers. I'm not sure what really does what but I need someone to pick out some stuff for me that is preferably not too much over $500. I would like a stereo that is iPod compatible if it's not to expensive and will work with all the other stuff (like speakers and what not). I don't know what will work together and what won't. Also I don't what will work since it's an old car. If it will help, here is a picture of the current dashboard stereo. It has a tape player and a CD player.

http://s753.photobucket.com/albums/xx178/DownWithTheClown/Mobile%20Uploads/?action=view&current=Photo0085.jpg

Ask any questions if you need.

Also if you could explain what does what

Thanks