But all that's on the surface. The whole movie can be seen as an allegory for humans self-destructive behavior - that our tools we create end up destroying us (hence the famous cut from the bone to the nuclear hub in space, not to mention HAL). I've always preferred the more metaphorical explanation, or even a religious one. People forget that Kubrick was very religious. Here's one explanation:

Dave (along with all humans) want to find out the answers to things, that's why they do everything they do. They see something they can't explain (monolith [religion/god/nature]) and they do everything they can to find out what it is, or what is all means. They even go to the edges of the solar system to find the answers, and still get none. It isn't until he dies, and is in the presence of god, that all is revealed to him in the form of the Star Child. I'm not religious by any means, but again, it's just one of many, many interpretations.

If you really want some crazy interpretations, watch it on shrooms - it was like seeing it for the first time!