Can someone explain to me why there is such a thing as DVD-RAM? I'm assuming RAM is the DVD media with the cartridge (I think there are some without). What is the difference between DVD-R, DVD+RW, and ...

ok, here's the real thing, none of my co-workers crap. I'm interested in getting a DVD-RAM drive. Here are my reasons, now could you guys help me figure out if it's right for me. I need a DVD player ...