Question about comic making and copyrights.

So uhh, I think I have to start from the beginning so you get the idea what I mean.

I love comics and have been wanting to make one for a.. well, a very long time already. But I have this problem that I'm not very good writer (actually I'm quite horrible at that.. : D) and to me it's very hard to came up with good and interesting stories/scripts. I'm more like the person who would like to draw comics, but with script/story which is written by someone else.

And now we come to my question.
I have been reading very good book lately and now I was wondering that would I be violating copyright rules if I make a comic which is based to that book? I mean like that if I use the book as a script to that comic. I know that if I do it just to my own amusement and experiment it's ok, but what if I would like to show it on internet? For example here or Smack Jeeves, ect.? And I also know that if I would publish it and sell it, THEN it would be against the copyright rules, but of course I have NO intentions to do like that. I just would like to do it for fun and for experiment, like I said before.

But what do you think, is that okay or not?