I have found the chk_poison module to be unreliable at best. Have you actually checked any of the victim machines to see if they have indeed been poisoned? It also may help to know what you are trying to accomplish. For instance, unless you are attempting a MITM attack you don't need to turn on IP forwarding. Also, until you have narrowed down the problem I would suggest attacking just one machine at a time. Also also, to say there is a wealth of videos online about this subject would be quite the understatement. The only other subject I can think of that has more tutorials and how-to's would WEP cracking. Google, as per usual, is ever useful.