Do you mean the entire thread or just the individual post?
If you want the entire thread, click on the thread and highlight the URL and copy it, then paste it into the thread of your choice.
I use firefox and I right click on the link and select Copy Link Location, then paste it into the thread of my choice.
Example:
http://www.blackberryforums.com/site...st-thread.html
If it is just one post out of a thread you want, click on the word Permalink at the top of the post, that will give you the URL to that post. Again, with Fire Fox you can use the Copy Link Location without having to actually open the link.
Example:
http://www.blackberryforums.com/site...ml#post1510126
Lastly, if you just want to show that post without the rest of the thread, click on the post number (to the left of the word permalink).
Example:
http://www.blackberryforums.com/1510114-post1.html