h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I have heard about the Astral Plane and Astral projection for some years now, so having read this guide entry, I was quite intrigued into practicing myself, However I would like some more info before I go jumping in without knowing the full story:

1) In this guide entry it mentions voices which encourage and voices which tell the projector to stop. Where do these voices come from and should they be heeded?
2)I have heard that the Astral Plane and astral projection, have been connected to the occult. Is this true and just how deep is the connection if there is any?
3) How long, on average, does it usually take a beginner to start projecting properly?
4) Are any problems that can occur from a "bad" astral experience?

I know that there are many powers in this world that should not be played with, but if dreaming is a form of astral projecting perhaps it isn't so bad, but I would rather be sure than make a terrible mistake. Could anyone suggest any books or sites that can explain this in greater detail? I would appreciate it. Thank you.