This thread, despite it's hiccups, might help you....
http://forums.b2evolution.net/viewtopic.php?t=18250&highlight=comments

You were right - the thread was quite disorganized, but I managed to come right eventually!

One thing though - I see it displays the "Leave a comment box" at the bottom of the comments. Is there a way to have only a button for leaving comments, instead of whole box?

Thanks for your help!

You could use some Jquery show/hide script to reveal the comment box, but I can't see any good usability reason why you would do that.

You have your comment discussion in full view and now you expect the next potential commenter to have to click something else just for the privilege of posting a comment on your blog.

In the photoblog skin, the comment box is a popup.
Maybe you could look at that configuration as a solution.

Very good idea! Thanks again.