2 ways to do this.
First get the specific reference. Call up the book on the screen, and place your cursor over the www. at top of screen. Copy the link. [left click mouse on the bar, it should turn blue. right click mouse and choose COPY} Now, follow below instructions.
If you are referring to a book in a JOURNAL entry (ie in a release note or in your journal about the book) use this formula:
<a href="PASTE YOUR LINK HERE">Book Title</a>
EXAMPLE so your journal might read
I read this wonderful book <a href= "http://www.bookcrossing.com/journal/13211062"> Dark Shadows Falling</a>, I really liked it. (click on link to see clean references this way in that journal)
Okay. That's for journal entries. Now for the forums. The a href WON'T work cleanly. It will look like above. Ugly (but still working). So it is easier. you just say
I read this wonderful book, Dark Shadows Falling http://www.bookcrossing.com/---/13211062
Fairly easy. The only cursing involved is when you write a long forum entry using the a href formula, and realize once it's posted that 'oops' the clean formula only works on journals.